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 $53.61   7.591%   $57.6795   $57.68   $57.70   $57.70  
  Purchase #2 $248.41   12.160%   $278.6167   $278.62   $278.60   $278.60  
  Purchase #3 $149.94   11.318%   $166.9102   $166.91   $166.90   $166.90  
  Purchase #4 $24.53   5.731%   $25.9358   $25.94   $25.95   $25.90  
  Purchase #5 $64.78   12.841%   $73.0984   $73.10   $73.10   $73.10  
  Purchase #6 $94.97   8.138%   $102.6987   $102.70   $102.70   $102.70  
  Purchase #7 $228.89   5.127%   $240.6252   $240.63   $240.65   $240.60  
  7 purchase totals = $865.13       $945.5645   $945.58   $945.60   $945.50