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 $33.83   7.411%   $36.3371   $36.34   $36.35   $36.30  
  Purchase #2 $8.28   3.658%   $8.5829   $8.58   $8.60   $8.60  
  Purchase #3 $223.64   13.511%   $253.856   $253.86   $253.85   $253.90  
  Purchase #4 $125.65   7.683%   $135.3037   $135.30   $135.30   $135.30  
  Purchase #5 $204.25   6.329%   $217.177   $217.18   $217.20   $217.20  
  Purchase #6 $121.31   9.856%   $133.2663   $133.27   $133.25   $133.30  
  Purchase #7 $10.33   5.634%   $10.912   $10.91   $10.90   $10.90  
  7 purchase totals = $727.29       $795.4350   $795.44   $795.45   $795.50