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 $62.86   5.572%   $66.3626   $66.36   $66.35   $66.40  
  Purchase #2 $236.95   13.352%   $268.5876   $268.59   $268.60   $268.60  
  Purchase #3 $50.49   13.290%   $57.2001   $57.20   $57.20   $57.20  
  Purchase #4 $68.93   5.462%   $72.695   $72.70   $72.70   $72.70  
  Purchase #5 $95.55   12.448%   $107.4441   $107.44   $107.45   $107.40  
  Purchase #6 $83.82   12.410%   $94.2221   $94.22   $94.20   $94.20  
  Purchase #7 $163.30   8.709%   $177.5218   $177.52   $177.50   $177.50  
  7 purchase totals = $761.90       $844.0333   $844.03   $844.00   $844.00