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 $135.39   9.401%   $148.118   $148.12   $148.10   $148.10  
  Purchase #2 $44.83   8.342%   $48.5697   $48.57   $48.55   $48.60  
  Purchase #3 $46.75   12.514%   $52.6003   $52.60   $52.60   $52.60  
  Purchase #4 $129.56   6.110%   $137.4761   $137.48   $137.50   $137.50  
  Purchase #5 $111.99   6.646%   $119.4329   $119.43   $119.45   $119.40  
  Purchase #6 $183.34   13.431%   $207.9644   $207.96   $207.95   $208.00  
  Purchase #7 $229.95   3.292%   $237.52   $237.52   $237.50   $237.50  
  7 purchase totals = $881.81       $951.6814   $951.68   $951.65   $951.70