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 $60.28   10.496%   $66.607   $66.61   $66.60   $66.60  
  Purchase #2 $123.52   3.496%   $127.8383   $127.84   $127.85   $127.80  
  Purchase #3 $26.30   8.607%   $28.5636   $28.56   $28.55   $28.60  
  Purchase #4 $210.70   12.386%   $236.7973   $236.80   $236.80   $236.80  
  Purchase #5 $22.96   5.840%   $24.3009   $24.30   $24.30   $24.30  
  Purchase #6 $205.88   4.187%   $214.5002   $214.50   $214.50   $214.50  
  Purchase #7 $55.44   13.144%   $62.727   $62.73   $62.75   $62.70  
  7 purchase totals = $705.08       $761.3343   $761.34   $761.35   $761.30