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 $125.85   8.576%   $136.6429   $136.64   $136.65   $136.60  
  Purchase #2 $70.35   5.127%   $73.9568   $73.96   $73.95   $74.00  
  Purchase #3 $95.36   6.308%   $101.3753   $101.38   $101.40   $101.40  
  Purchase #4 $204.27   7.379%   $219.3431   $219.34   $219.35   $219.30  
  Purchase #5 $211.85   6.488%   $225.5948   $225.59   $225.60   $225.60  
  Purchase #6 $54.45   9.233%   $59.4774   $59.48   $59.50   $59.50  
  Purchase #7 $125.43   9.866%   $137.8049   $137.80   $137.80   $137.80  
  7 purchase totals = $887.56       $954.1952   $954.19   $954.25   $954.20