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 $56.66   4.644%   $59.2913   $59.29   $59.30   $59.30  
  Purchase #2 $215.27   12.236%   $241.6104   $241.61   $241.60   $241.60  
  Purchase #3 $123.53   9.184%   $134.875   $134.88   $134.90   $134.90  
  Purchase #4 $158.84   7.436%   $170.6513   $170.65   $170.65   $170.70  
  Purchase #5 $112.96   4.637%   $118.198   $118.20   $118.20   $118.20  
  Purchase #6 $136.64   10.790%   $151.3835   $151.38   $151.40   $151.40  
  Purchase #7 $17.39   10.617%   $19.2363   $19.24   $19.25   $19.20  
  7 purchase totals = $821.29       $895.2458   $895.25   $895.30   $895.30