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 $229.68   9.318%   $251.0816   $251.08   $251.10   $251.10  
  Purchase #2 $43.39   6.698%   $46.2963   $46.30   $46.30   $46.30  
  Purchase #3 $119.78   8.317%   $129.7421   $129.74   $129.75   $129.70  
  Purchase #4 $184.87   8.399%   $200.3972   $200.40   $200.40   $200.40  
  Purchase #5 $237.76   3.243%   $245.4706   $245.47   $245.45   $245.50  
  Purchase #6 $20.72   9.276%   $22.642   $22.64   $22.65   $22.60  
  Purchase #7 $57.79   10.833%   $64.0504   $64.05   $64.05   $64.10  
  7 purchase totals = $893.99       $959.6802   $959.68   $959.70   $959.70