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 $179.98   8.669%   $195.5825   $195.58   $195.60   $195.60  
  Purchase #2 $133.79   13.355%   $151.6577   $151.66   $151.65   $151.70  
  Purchase #3 $41.73   11.608%   $46.574   $46.57   $46.55   $46.60  
  Purchase #4 $142.91   13.319%   $161.9442   $161.94   $161.95   $161.90  
  Purchase #5 $18.74   13.630%   $21.2943   $21.29   $21.30   $21.30  
  Purchase #6 $94.86   11.779%   $106.0336   $106.03   $106.05   $106.00  
  Purchase #7 $191.32   12.713%   $215.6425   $215.64   $215.65   $215.60  
  7 purchase totals = $803.33       $898.7288   $898.71   $898.75   $898.70