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 $85.92   10.357%   $94.8187   $94.82   $94.80   $94.80  
  Purchase #2 $65.59   8.341%   $71.0609   $71.06   $71.05   $71.10  
  Purchase #3 $63.49   8.213%   $68.7044   $68.70   $68.70   $68.70  
  Purchase #4 $71.87   3.546%   $74.4185   $74.42   $74.40   $74.40  
  Purchase #5 $222.77   6.806%   $237.9317   $237.93   $237.95   $237.90  
  Purchase #6 $22.65   6.808%   $24.192   $24.19   $24.20   $24.20  
  Purchase #7 $218.30   10.789%   $241.8524   $241.85   $241.85   $241.90  
  7 purchase totals = $750.59       $812.9786   $812.97   $812.95   $813.00