Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $227.71   7.285%   $244.2987   $244.30   $244.30   $244.30  
  Purchase #2 $106.72   9.463%   $116.8189   $116.82   $116.80   $116.80  
  Purchase #3 $147.30   11.694%   $164.5253   $164.53   $164.55   $164.50  
  Purchase #4 $227.84   13.868%   $259.4369   $259.44   $259.45   $259.40  
  Purchase #5 $208.80   8.362%   $226.2599   $226.26   $226.25   $226.30  
  Purchase #6 $156.71   9.611%   $171.7714   $171.77   $171.75   $171.80  
  Purchase #7 $116.51   7.217%   $124.9185   $124.92   $124.90   $124.90  
  7 purchase totals = $1,191.59       $1,308.0296   $1,308.04   $1,308.00   $1,308.00