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 $67.51   13.162%   $76.3957   $76.40   $76.40   $76.40  
  Purchase #2 $209.27   6.170%   $222.182   $222.18   $222.20   $222.20  
  Purchase #3 $127.72   9.504%   $139.8585   $139.86   $139.85   $139.90  
  Purchase #4 $135.94   10.483%   $150.1906   $150.19   $150.20   $150.20  
  Purchase #5 $17.54   4.257%   $18.2867   $18.29   $18.30   $18.30  
  Purchase #6 $41.46   7.645%   $44.6296   $44.63   $44.65   $44.60  
  Purchase #7 $221.37   11.460%   $246.739   $246.74   $246.75   $246.70  
  7 purchase totals = $820.81       $898.2821   $898.29   $898.35   $898.30