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 $119.66   6.102%   $126.9617   $126.96   $126.95   $127.00  
  Purchase #2 $221.79   9.737%   $243.3857   $243.39   $243.40   $243.40  
  Purchase #3 $162.36   5.392%   $171.1145   $171.11   $171.10   $171.10  
  Purchase #4 $132.33   5.665%   $139.8265   $139.83   $139.85   $139.80  
  Purchase #5 $203.90   6.251%   $216.6458   $216.65   $216.65   $216.60  
  Purchase #6 $162.77   6.803%   $173.8432   $173.84   $173.85   $173.80  
  Purchase #7 $148.26   12.376%   $166.6087   $166.61   $166.60   $166.60  
  7 purchase totals = $1,151.07       $1,238.3861   $1,238.39   $1,238.40   $1,238.30