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 $84.97   13.467%   $96.4129   $96.41   $96.40   $96.40  
  Purchase #2 $59.67   11.841%   $66.7355   $66.74   $66.75   $66.70  
  Purchase #3 $158.79   3.197%   $163.8665   $163.87   $163.85   $163.90  
  Purchase #4 $45.33   8.599%   $49.2279   $49.23   $49.25   $49.20  
  Purchase #5 $241.84   5.164%   $254.3286   $254.33   $254.35   $254.30  
  Purchase #6 $49.49   13.160%   $56.0029   $56.00   $56.00   $56.00  
  Purchase #7 $64.54   10.603%   $71.3832   $71.38   $71.40   $71.40  
  7 purchase totals = $704.63       $757.9575   $757.96   $758.00   $757.90