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 $57.68   8.479%   $62.5707   $62.57   $62.55   $62.60  
  Purchase #2 $211.55   13.519%   $240.1494   $240.15   $240.15   $240.10  
  Purchase #3 $23.47   7.402%   $25.2072   $25.21   $25.20   $25.20  
  Purchase #4 $46.56   3.328%   $48.1095   $48.11   $48.10   $48.10  
  Purchase #5 $155.96   3.461%   $161.3578   $161.36   $161.35   $161.40  
  Purchase #6 $228.72   12.717%   $257.8063   $257.81   $257.80   $257.80  
  Purchase #7 $127.64   11.612%   $142.4616   $142.46   $142.45   $142.50  
  7 purchase totals = $851.58       $937.6625   $937.67   $937.60   $937.70