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 $134.53   9.215%   $146.9269   $146.93   $146.95   $146.90  
  Purchase #2 $92.54   5.513%   $97.6417   $97.64   $97.65   $97.60  
  Purchase #3 $14.93   3.546%   $15.4594   $15.46   $15.45   $15.50  
  Purchase #4 $165.37   6.212%   $175.6428   $175.64   $175.65   $175.60  
  Purchase #5 $43.48   12.297%   $48.8267   $48.83   $48.85   $48.80  
  Purchase #6 $46.52   10.843%   $51.5642   $51.56   $51.55   $51.60  
  Purchase #7 $240.56   3.734%   $249.5425   $249.54   $249.55   $249.50  
  7 purchase totals = $737.93       $785.6042   $785.60   $785.65   $785.50