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 $47.97   11.737%   $53.6002   $53.60   $53.60   $53.60  
  Purchase #2 $19.96   10.199%   $21.9957   $22.00   $22.00   $22.00  
  Purchase #3 $180.53   9.294%   $197.3085   $197.31   $197.30   $197.30  
  Purchase #4 $115.88   7.141%   $124.155   $124.16   $124.15   $124.20  
  Purchase #5 $182.85   9.169%   $199.6155   $199.62   $199.60   $199.60  
  Purchase #6 $175.79   10.418%   $194.1038   $194.10   $194.10   $194.10  
  Purchase #7 $212.40   8.206%   $229.8295   $229.83   $229.85   $229.80  
  7 purchase totals = $935.38       $1,020.6082   $1,020.62   $1,020.60   $1,020.60