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 $54.28   13.312%   $61.5058   $61.51   $61.50   $61.50  
  Purchase #2 $123.61   12.667%   $139.2677   $139.27   $139.25   $139.30  
  Purchase #3 $207.65   3.608%   $215.142   $215.14   $215.15   $215.10  
  Purchase #4 $212.77   5.137%   $223.7   $223.70   $223.70   $223.70  
  Purchase #5 $44.86   6.860%   $47.9374   $47.94   $47.95   $47.90  
  Purchase #6 $103.78   6.201%   $110.2154   $110.22   $110.20   $110.20  
  Purchase #7 $202.92   11.130%   $225.505   $225.51   $225.50   $225.50  
  7 purchase totals = $949.87       $1,023.2733   $1,023.29   $1,023.25   $1,023.20