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 $191.67   5.252%   $201.7365   $201.74   $201.75   $201.70  
  Purchase #2 $32.30   4.380%   $33.7147   $33.71   $33.70   $33.70  
  Purchase #3 $18.39   3.438%   $19.0222   $19.02   $19.00   $19.00  
  Purchase #4 $226.96   3.111%   $234.0207   $234.02   $234.00   $234.00  
  Purchase #5 $168.61   3.650%   $174.7643   $174.76   $174.75   $174.80  
  Purchase #6 $113.71   9.593%   $124.6182   $124.62   $124.60   $124.60  
  Purchase #7 $55.94   9.534%   $61.2733   $61.27   $61.25   $61.30  
  7 purchase totals = $807.58       $849.1499   $849.14   $849.05   $849.10