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 $96.90   13.731%   $110.2053   $110.21   $110.20   $110.20  
  Purchase #2 $140.89   9.548%   $154.3422   $154.34   $154.35   $154.30  
  Purchase #3 $224.51   7.530%   $241.4156   $241.42   $241.40   $241.40  
  Purchase #4 $223.72   9.442%   $244.8436   $244.84   $244.85   $244.80  
  Purchase #5 $66.32   7.355%   $71.1978   $71.20   $71.20   $71.20  
  Purchase #6 $236.48   3.123%   $243.8653   $243.87   $243.85   $243.90  
  Purchase #7 $176.77   13.646%   $200.892   $200.89   $200.90   $200.90  
  7 purchase totals = $1,165.59       $1,266.7618   $1,266.77   $1,266.75   $1,266.70