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 $156.89   11.556%   $175.0202   $175.02   $175.00   $175.00  
  Purchase #2 $23.62   8.186%   $25.5535   $25.55   $25.55   $25.60  
  Purchase #3 $74.63   5.573%   $78.7891   $78.79   $78.80   $78.80  
  Purchase #4 $169.81   9.690%   $186.2646   $186.26   $186.25   $186.30  
  Purchase #5 $164.91   9.303%   $180.2516   $180.25   $180.25   $180.30  
  Purchase #6 $205.85   3.448%   $212.9477   $212.95   $212.95   $212.90  
  Purchase #7 $74.40   10.558%   $82.2552   $82.26   $82.25   $82.30  
  7 purchase totals = $870.11       $941.0819   $941.08   $941.05   $941.20