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 $84.68   10.434%   $93.5155   $93.52   $93.50   $93.50  
  Purchase #2 $43.30   13.527%   $49.1572   $49.16   $49.15   $49.20  
  Purchase #3 $82.28   7.477%   $88.4321   $88.43   $88.45   $88.40  
  Purchase #4 $26.68   7.787%   $28.7576   $28.76   $28.75   $28.80  
  Purchase #5 $47.88   9.858%   $52.6   $52.60   $52.60   $52.60  
  Purchase #6 $180.78   7.293%   $193.9643   $193.96   $193.95   $194.00  
  Purchase #7 $225.92   3.833%   $234.5795   $234.58   $234.60   $234.60  
  7 purchase totals = $691.52       $741.0062   $741.01   $741.00   $741.10