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 $65.33   6.466%   $69.5542   $69.55   $69.55   $69.60  
  Purchase #2 $185.77   6.221%   $197.3268   $197.33   $197.35   $197.30  
  Purchase #3 $158.28   10.646%   $175.1305   $175.13   $175.15   $175.10  
  Purchase #4 $144.30   3.178%   $148.8859   $148.89   $148.90   $148.90  
  Purchase #5 $139.82   12.286%   $156.9983   $157.00   $157.00   $157.00  
  Purchase #6 $248.93   3.647%   $258.0085   $258.01   $258.00   $258.00  
  Purchase #7 $218.70   10.676%   $242.0484   $242.05   $242.05   $242.00  
  7 purchase totals = $1,161.13       $1,247.9526   $1,247.96   $1,248.00   $1,247.90