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 $186.64   11.416%   $207.9468   $207.95   $207.95   $207.90  
  Purchase #2 $40.31   10.259%   $44.4454   $44.45   $44.45   $44.40  
  Purchase #3 $46.27   9.609%   $50.7161   $50.72   $50.70   $50.70  
  Purchase #4 $94.26   12.313%   $105.8662   $105.87   $105.85   $105.90  
  Purchase #5 $94.94   12.427%   $106.7382   $106.74   $106.75   $106.70  
  Purchase #6 $72.70   3.611%   $75.3252   $75.33   $75.35   $75.30  
  Purchase #7 $241.97   12.395%   $271.9622   $271.96   $271.95   $272.00  
  7 purchase totals = $777.09       $863.0001   $863.02   $863.00   $862.90