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 $43.86   7.867%   $47.3105   $47.31   $47.30   $47.30  
  Purchase #2 $205.85   5.431%   $217.0297   $217.03   $217.05   $217.00  
  Purchase #3 $24.34   13.843%   $27.7094   $27.71   $27.70   $27.70  
  Purchase #4 $95.62   11.448%   $106.5666   $106.57   $106.55   $106.60  
  Purchase #5 $232.98   9.576%   $255.2902   $255.29   $255.30   $255.30  
  Purchase #6 $247.74   4.429%   $258.7124   $258.71   $258.70   $258.70  
  Purchase #7 $46.35   12.500%   $52.1438   $52.14   $52.15   $52.10  
  7 purchase totals = $896.74       $964.7626   $964.76   $964.75   $964.70