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 $182.34   12.293%   $204.7551   $204.76   $204.75   $204.80  
  Purchase #2 $243.61   10.217%   $268.4996   $268.50   $268.50   $268.50  
  Purchase #3 $230.47   11.710%   $257.458   $257.46   $257.45   $257.50  
  Purchase #4 $32.76   5.666%   $34.6162   $34.62   $34.60   $34.60  
  Purchase #5 $176.56   7.354%   $189.5442   $189.54   $189.55   $189.50  
  Purchase #6 $117.99   12.292%   $132.4933   $132.49   $132.50   $132.50  
  Purchase #7 $68.60   9.309%   $74.986   $74.99   $75.00   $75.00  
  7 purchase totals = $1,052.33       $1,162.3524   $1,162.36   $1,162.35   $1,162.40