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 $82.70   12.527%   $93.0598   $93.06   $93.05   $93.10  
  Purchase #2 $116.52   7.237%   $124.9526   $124.95   $124.95   $125.00  
  Purchase #3 $178.57   8.271%   $193.3395   $193.34   $193.35   $193.30  
  Purchase #4 $128.25   4.294%   $133.7571   $133.76   $133.75   $133.80  
  Purchase #5 $136.53   12.578%   $153.7027   $153.70   $153.70   $153.70  
  Purchase #6 $192.87   12.345%   $216.6798   $216.68   $216.70   $216.70  
  Purchase #7 $118.39   6.460%   $126.038   $126.04   $126.05   $126.00  
  7 purchase totals = $953.83       $1,041.5295   $1,041.53   $1,041.55   $1,041.60