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 $225.67   11.314%   $251.2023   $251.20   $251.20   $251.20  
  Purchase #2 $189.82   12.583%   $213.7051   $213.71   $213.70   $213.70  
  Purchase #3 $166.98   3.299%   $172.4887   $172.49   $172.50   $172.50  
  Purchase #4 $33.66   9.145%   $36.7382   $36.74   $36.75   $36.70  
  Purchase #5 $95.95   3.488%   $99.2967   $99.30   $99.30   $99.30  
  Purchase #6 $58.62   10.394%   $64.713   $64.71   $64.70   $64.70  
  Purchase #7 $189.50   8.231%   $205.0977   $205.10   $205.10   $205.10  
  7 purchase totals = $960.20       $1,043.2417   $1,043.25   $1,043.25   $1,043.20