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 $234.47   5.304%   $246.9063   $246.91   $246.90   $246.90  
  Purchase #2 $233.27   7.580%   $250.9519   $250.95   $250.95   $251.00  
  Purchase #3 $110.43   13.781%   $125.6484   $125.65   $125.65   $125.60  
  Purchase #4 $42.42   13.792%   $48.2706   $48.27   $48.25   $48.30  
  Purchase #5 $97.72   7.289%   $104.8428   $104.84   $104.85   $104.80  
  Purchase #6 $29.93   13.830%   $34.0693   $34.07   $34.05   $34.10  
  Purchase #7 $232.33   3.561%   $240.6033   $240.60   $240.60   $240.60  
  7 purchase totals = $980.57       $1,051.2926   $1,051.29   $1,051.25   $1,051.30