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 $35.53   5.770%   $37.5801   $37.58   $37.60   $37.60  
  Purchase #2 $173.57   11.285%   $193.1574   $193.16   $193.15   $193.20  
  Purchase #3 $138.50   9.792%   $152.0619   $152.06   $152.05   $152.10  
  Purchase #4 $121.35   11.455%   $135.2506   $135.25   $135.25   $135.30  
  Purchase #5 $250.76   7.627%   $269.8855   $269.89   $269.90   $269.90  
  Purchase #6 $13.42   4.857%   $14.0718   $14.07   $14.05   $14.10  
  Purchase #7 $170.58   5.266%   $179.5627   $179.56   $179.55   $179.60  
  7 purchase totals = $903.71       $981.5700   $981.57   $981.55   $981.80