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 $94.67   12.111%   $106.1355   $106.14   $106.15   $106.10  
  Purchase #2 $56.78   13.866%   $64.6531   $64.65   $64.65   $64.70  
  Purchase #3 $40.98   7.834%   $44.1904   $44.19   $44.20   $44.20  
  Purchase #4 $92.29   10.253%   $101.7525   $101.75   $101.75   $101.80  
  Purchase #5 $56.79   10.584%   $62.8007   $62.80   $62.80   $62.80  
  Purchase #6 $250.83   5.771%   $265.3054   $265.31   $265.30   $265.30  
  Purchase #7 $111.76   8.341%   $121.0819   $121.08   $121.10   $121.10  
  7 purchase totals = $704.10       $765.9195   $765.92   $765.95   $766.00