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 $244.76   9.470%   $267.9388   $267.94   $267.95   $267.90  
  Purchase #2 $48.71   11.793%   $54.4544   $54.45   $54.45   $54.50  
  Purchase #3 $126.89   13.822%   $144.4287   $144.43   $144.45   $144.40  
  Purchase #4 $192.25   4.688%   $201.2627   $201.26   $201.25   $201.30  
  Purchase #5 $120.45   10.395%   $132.9708   $132.97   $132.95   $133.00  
  Purchase #6 $132.41   7.265%   $142.0296   $142.03   $142.05   $142.00  
  Purchase #7 $65.30   11.852%   $73.0394   $73.04   $73.05   $73.00  
  7 purchase totals = $930.77       $1,016.1244   $1,016.12   $1,016.15   $1,016.10