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 $208.45   12.863%   $235.2629   $235.26   $235.25   $235.30  
  Purchase #2 $54.49   11.871%   $60.9585   $60.96   $60.95   $61.00  
  Purchase #3 $118.71   13.236%   $134.4225   $134.42   $134.40   $134.40  
  Purchase #4 $91.27   12.654%   $102.8193   $102.82   $102.80   $102.80  
  Purchase #5 $80.74   3.380%   $83.469   $83.47   $83.45   $83.50  
  Purchase #6 $67.66   12.398%   $76.0485   $76.05   $76.05   $76.00  
  Purchase #7 $135.78   12.215%   $152.3655   $152.37   $152.35   $152.40  
  7 purchase totals = $757.10       $845.3462   $845.35   $845.25   $845.40