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 $250.47   5.824%   $265.0574   $265.06   $265.05   $265.10  
  Purchase #2 $131.75   12.647%   $148.4124   $148.41   $148.40   $148.40  
  Purchase #3 $47.91   13.459%   $54.3582   $54.36   $54.35   $54.40  
  Purchase #4 $53.38   8.528%   $57.9322   $57.93   $57.95   $57.90  
  Purchase #5 $162.55   7.345%   $174.4893   $174.49   $174.50   $174.50  
  Purchase #6 $241.86   11.374%   $269.3692   $269.37   $269.35   $269.40  
  Purchase #7 $89.71   4.752%   $93.973   $93.97   $93.95   $94.00  
  7 purchase totals = $977.63       $1,063.5917   $1,063.59   $1,063.55   $1,063.70