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 $78.52   12.743%   $88.5258   $88.53   $88.55   $88.50  
  Purchase #2 $95.65   5.348%   $100.7654   $100.77   $100.75   $100.80  
  Purchase #3 $238.79   3.205%   $246.4432   $246.44   $246.45   $246.40  
  Purchase #4 $26.78   13.194%   $30.3134   $30.31   $30.30   $30.30  
  Purchase #5 $64.35   6.462%   $68.5083   $68.51   $68.50   $68.50  
  Purchase #6 $159.64   11.851%   $178.5589   $178.56   $178.55   $178.60  
  Purchase #7 $234.74   3.682%   $243.3831   $243.38   $243.40   $243.40  
  7 purchase totals = $898.47       $956.4981   $956.50   $956.50   $956.50