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 $187.42   6.851%   $200.2601   $200.26   $200.25   $200.30  
  Purchase #2 $236.90   4.230%   $246.9209   $246.92   $246.90   $246.90  
  Purchase #3 $217.82   6.198%   $231.3205   $231.32   $231.30   $231.30  
  Purchase #4 $157.68   7.682%   $169.793   $169.79   $169.80   $169.80  
  Purchase #5 $210.31   6.753%   $224.5122   $224.51   $224.50   $224.50  
  Purchase #6 $48.41   13.345%   $54.8703   $54.87   $54.85   $54.90  
  Purchase #7 $250.65   9.386%   $274.176   $274.18   $274.20   $274.20  
  7 purchase totals = $1,309.19       $1,401.8530   $1,401.85   $1,401.80   $1,401.90