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 $64.64   7.711%   $69.6244   $69.62   $69.60   $69.60  
  Purchase #2 $208.45   9.480%   $228.2111   $228.21   $228.20   $228.20  
  Purchase #3 $150.67   7.826%   $162.4614   $162.46   $162.45   $162.50  
  Purchase #4 $19.44   5.415%   $20.4927   $20.49   $20.50   $20.50  
  Purchase #5 $178.27   12.584%   $200.7035   $200.70   $200.70   $200.70  
  Purchase #6 $107.78   4.545%   $112.6786   $112.68   $112.70   $112.70  
  Purchase #7 $213.87   12.319%   $240.2166   $240.22   $240.20   $240.20  
  7 purchase totals = $943.12       $1,034.3883   $1,034.38   $1,034.35   $1,034.40