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 $242.88   4.493%   $253.7926   $253.79   $253.80   $253.80  
  Purchase #2 $177.85   13.774%   $202.3471   $202.35   $202.35   $202.30  
  Purchase #3 $123.62   11.424%   $137.7423   $137.74   $137.75   $137.70  
  Purchase #4 $169.70   12.802%   $191.425   $191.43   $191.45   $191.40  
  Purchase #5 $198.37   3.325%   $204.9658   $204.97   $204.95   $205.00  
  Purchase #6 $90.46   8.614%   $98.2522   $98.25   $98.25   $98.30  
  Purchase #7 $85.44   12.170%   $95.838   $95.84   $95.85   $95.80  
  7 purchase totals = $1,088.32       $1,184.3630   $1,184.37   $1,184.40   $1,184.30