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 $183.61   11.210%   $204.1927   $204.19   $204.20   $204.20  
  Purchase #2 $136.67   5.247%   $143.8411   $143.84   $143.85   $143.80  
  Purchase #3 $56.83   12.589%   $63.9843   $63.98   $64.00   $64.00  
  Purchase #4 $188.31   10.389%   $207.8735   $207.87   $207.85   $207.90  
  Purchase #5 $56.47   13.413%   $64.0443   $64.04   $64.05   $64.00  
  Purchase #6 $227.51   11.162%   $252.9047   $252.90   $252.90   $252.90  
  Purchase #7 $183.78   11.485%   $204.8871   $204.89   $204.90   $204.90  
  7 purchase totals = $1,033.18       $1,141.7277   $1,141.71   $1,141.75   $1,141.70