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 $243.53   5.377%   $256.6246   $256.62   $256.60   $256.60  
  Purchase #2 $219.28   6.327%   $233.1538   $233.15   $233.15   $233.20  
  Purchase #3 $238.61   12.402%   $268.2024   $268.20   $268.20   $268.20  
  Purchase #4 $233.55   12.638%   $263.066   $263.07   $263.05   $263.10  
  Purchase #5 $197.98   10.459%   $218.6867   $218.69   $218.70   $218.70  
  Purchase #6 $179.42   8.134%   $194.014   $194.01   $194.00   $194.00  
  Purchase #7 $115.94   10.582%   $128.2088   $128.21   $128.20   $128.20  
  7 purchase totals = $1,428.31       $1,561.9563   $1,561.95   $1,561.90   $1,562.00