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 $238.74   6.399%   $254.017   $254.02   $254.00   $254.00  
  Purchase #2 $42.62   13.643%   $48.4346   $48.43   $48.45   $48.40  
  Purchase #3 $125.64   6.377%   $133.6521   $133.65   $133.65   $133.70  
  Purchase #4 $175.40   10.832%   $194.3993   $194.40   $194.40   $194.40  
  Purchase #5 $90.25   13.462%   $102.3995   $102.40   $102.40   $102.40  
  Purchase #6 $52.52   5.457%   $55.386   $55.39   $55.40   $55.40  
  Purchase #7 $230.43   6.808%   $246.1177   $246.12   $246.10   $246.10  
  7 purchase totals = $955.60       $1,034.4062   $1,034.41   $1,034.40   $1,034.40