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 $234.59   10.862%   $260.0712   $260.07   $260.05   $260.10  
  Purchase #2 $121.25   3.686%   $125.7193   $125.72   $125.70   $125.70  
  Purchase #3 $164.98   9.184%   $180.1318   $180.13   $180.15   $180.10  
  Purchase #4 $101.51   5.630%   $107.225   $107.23   $107.25   $107.20  
  Purchase #5 $143.55   4.157%   $149.5174   $149.52   $149.50   $149.50  
  Purchase #6 $17.90   10.698%   $19.8149   $19.81   $19.80   $19.80  
  Purchase #7 $120.49   3.841%   $125.118   $125.12   $125.10   $125.10  
  7 purchase totals = $904.27       $967.5976   $967.60   $967.55   $967.50