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 $55.33   12.131%   $62.0421   $62.04   $62.05   $62.00  
  Purchase #2 $78.79   7.826%   $84.9561   $84.96   $84.95   $85.00  
  Purchase #3 $171.90   4.871%   $180.2732   $180.27   $180.25   $180.30  
  Purchase #4 $92.93   6.296%   $98.7809   $98.78   $98.80   $98.80  
  Purchase #5 $144.42   11.575%   $161.1366   $161.14   $161.15   $161.10  
  Purchase #6 $166.26   9.233%   $181.6108   $181.61   $181.60   $181.60  
  Purchase #7 $201.94   7.769%   $217.6287   $217.63   $217.65   $217.60  
  7 purchase totals = $911.57       $986.4284   $986.43   $986.45   $986.40