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 $102.56   13.783%   $116.6958   $116.70   $116.70   $116.70  
  Purchase #2 $246.27   12.540%   $277.1523   $277.15   $277.15   $277.20  
  Purchase #3 $71.42   6.857%   $76.3173   $76.32   $76.30   $76.30  
  Purchase #4 $16.79   8.412%   $18.2024   $18.20   $18.20   $18.20  
  Purchase #5 $94.76   10.162%   $104.3895   $104.39   $104.40   $104.40  
  Purchase #6 $154.65   10.179%   $170.3918   $170.39   $170.40   $170.40  
  Purchase #7 $223.77   12.165%   $250.9916   $250.99   $251.00   $251.00  
  7 purchase totals = $910.22       $1,014.1407   $1,014.14   $1,014.15   $1,014.20