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 $205.53   10.769%   $227.6635   $227.66   $227.65   $227.70  
  Purchase #2 $134.64   3.871%   $139.8519   $139.85   $139.85   $139.90  
  Purchase #3 $54.45   13.605%   $61.8579   $61.86   $61.85   $61.90  
  Purchase #4 $85.31   7.628%   $91.8174   $91.82   $91.80   $91.80  
  Purchase #5 $241.59   4.772%   $253.1187   $253.12   $253.10   $253.10  
  Purchase #6 $163.68   3.714%   $169.7591   $169.76   $169.75   $169.80  
  Purchase #7 $81.76   12.799%   $92.2245   $92.22   $92.20   $92.20  
  7 purchase totals = $966.96       $1,036.2930   $1,036.29   $1,036.20   $1,036.40