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 $44.28   12.478%   $49.8053   $49.81   $49.80   $49.80  
  Purchase #2 $146.61   10.249%   $161.6361   $161.64   $161.65   $161.60  
  Purchase #3 $87.61   10.529%   $96.8345   $96.83   $96.85   $96.80  
  Purchase #4 $203.26   6.567%   $216.6081   $216.61   $216.60   $216.60  
  Purchase #5 $198.36   6.839%   $211.9258   $211.93   $211.95   $211.90  
  Purchase #6 $71.63   5.547%   $75.6033   $75.60   $75.60   $75.60  
  Purchase #7 $83.77   10.742%   $92.7686   $92.77   $92.75   $92.80  
  7 purchase totals = $835.52       $905.1817   $905.19   $905.20   $905.10