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 $112.53   13.373%   $127.5786   $127.58   $127.60   $127.60  
  Purchase #2 $95.43   7.587%   $102.6703   $102.67   $102.65   $102.70  
  Purchase #3 $158.94   11.835%   $177.7505   $177.75   $177.75   $177.80  
  Purchase #4 $64.56   6.353%   $68.6615   $68.66   $68.65   $68.70  
  Purchase #5 $166.93   3.746%   $173.1832   $173.18   $173.20   $173.20  
  Purchase #6 $14.40   9.127%   $15.7143   $15.71   $15.70   $15.70  
  Purchase #7 $60.40   4.495%   $63.115   $63.12   $63.10   $63.10  
  7 purchase totals = $673.19       $728.6734   $728.67   $728.65   $728.80