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 $64.41   6.658%   $68.6984   $68.70   $68.70   $68.70  
  Purchase #2 $153.69   5.409%   $162.0031   $162.00   $162.00   $162.00  
  Purchase #3 $45.68   6.724%   $48.7515   $48.75   $48.75   $48.80  
  Purchase #4 $164.67   8.297%   $178.3327   $178.33   $178.35   $178.30  
  Purchase #5 $129.50   13.804%   $147.3762   $147.38   $147.40   $147.40  
  Purchase #6 $49.37   13.184%   $55.8789   $55.88   $55.90   $55.90  
  Purchase #7 $95.31   5.237%   $100.3014   $100.30   $100.30   $100.30  
  7 purchase totals = $702.63       $761.3422   $761.34   $761.40   $761.40