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 $126.50   6.201%   $134.3443   $134.34   $134.35   $134.30  
  Purchase #2 $112.87   11.218%   $125.5318   $125.53   $125.55   $125.50  
  Purchase #3 $185.48   8.113%   $200.528   $200.53   $200.55   $200.50  
  Purchase #4 $213.55   10.179%   $235.2873   $235.29   $235.30   $235.30  
  Purchase #5 $242.87   8.550%   $263.6354   $263.64   $263.65   $263.60  
  Purchase #6 $48.59   13.687%   $55.2405   $55.24   $55.25   $55.20  
  Purchase #7 $162.94   4.852%   $170.8458   $170.85   $170.85   $170.80  
  7 purchase totals = $1,092.80       $1,185.4131   $1,185.42   $1,185.50   $1,185.20