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 $195.27   11.804%   $218.3197   $218.32   $218.30   $218.30  
  Purchase #2 $96.87   9.362%   $105.939   $105.94   $105.95   $105.90  
  Purchase #3 $65.96   12.494%   $74.201   $74.20   $74.20   $74.20  
  Purchase #4 $227.28   8.136%   $245.7715   $245.77   $245.75   $245.80  
  Purchase #5 $7.84   8.572%   $8.512   $8.51   $8.50   $8.50  
  Purchase #6 $245.32   9.146%   $267.757   $267.76   $267.75   $267.80  
  Purchase #7 $18.50   11.852%   $20.6926   $20.69   $20.70   $20.70  
  7 purchase totals = $857.04       $941.1928   $941.19   $941.15   $941.20