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 $66.82   13.385%   $75.7639   $75.76   $75.75   $75.80  
  Purchase #2 $237.61   13.153%   $268.8628   $268.86   $268.85   $268.90  
  Purchase #3 $56.70   7.711%   $61.0721   $61.07   $61.05   $61.10  
  Purchase #4 $121.97   8.820%   $132.7278   $132.73   $132.75   $132.70  
  Purchase #5 $116.82   7.655%   $125.7626   $125.76   $125.75   $125.80  
  Purchase #6 $231.36   8.640%   $251.3495   $251.35   $251.35   $251.30  
  Purchase #7 $12.84   9.320%   $14.0367   $14.04   $14.05   $14.00  
  7 purchase totals = $844.12       $929.5754   $929.57   $929.55   $929.60