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 $95.91   9.610%   $105.127   $105.13   $105.15   $105.10  
  Purchase #2 $47.65   3.587%   $49.3592   $49.36   $49.35   $49.40  
  Purchase #3 $49.63   13.551%   $56.3554   $56.36   $56.35   $56.40  
  Purchase #4 $61.28   9.443%   $67.0667   $67.07   $67.05   $67.10  
  Purchase #5 $84.48   4.291%   $88.105   $88.11   $88.10   $88.10  
  Purchase #6 $132.56   3.225%   $136.8351   $136.84   $136.85   $136.80  
  Purchase #7 $154.84   11.794%   $173.1018   $173.10   $173.10   $173.10  
  7 purchase totals = $626.35       $675.9502   $675.97   $675.95   $676.00