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 $243.34   3.226%   $251.1901   $251.19   $251.20   $251.20  
  Purchase #2 $237.46   8.541%   $257.7415   $257.74   $257.75   $257.70  
  Purchase #3 $23.29   4.390%   $24.3124   $24.31   $24.30   $24.30  
  Purchase #4 $82.72   3.262%   $85.4183   $85.42   $85.40   $85.40  
  Purchase #5 $100.55   5.667%   $106.2482   $106.25   $106.25   $106.20  
  Purchase #6 $163.80   3.382%   $169.3397   $169.34   $169.35   $169.30  
  Purchase #7 $63.81   8.283%   $69.0954   $69.10   $69.10   $69.10  
  7 purchase totals = $914.97       $963.3456   $963.35   $963.35   $963.20