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 $84.93   9.606%   $93.0884   $93.09   $93.10   $93.10  
  Purchase #2 $214.38   4.754%   $224.5716   $224.57   $224.55   $224.60  
  Purchase #3 $60.40   4.365%   $63.0365   $63.04   $63.05   $63.00  
  Purchase #4 $52.44   13.867%   $59.7119   $59.71   $59.70   $59.70  
  Purchase #5 $202.77   4.175%   $211.2356   $211.24   $211.25   $211.20  
  Purchase #6 $168.29   5.138%   $176.9367   $176.94   $176.95   $176.90  
  Purchase #7 $86.33   7.741%   $93.0128   $93.01   $93.00   $93.00  
  7 purchase totals = $869.54       $921.5935   $921.60   $921.60   $921.50