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 $116.53   8.470%   $126.4001   $126.40   $126.40   $126.40  
  Purchase #2 $172.86   13.239%   $195.7449   $195.74   $195.75   $195.70  
  Purchase #3 $65.71   3.274%   $67.8613   $67.86   $67.85   $67.90  
  Purchase #4 $154.50   9.829%   $169.6858   $169.69   $169.70   $169.70  
  Purchase #5 $216.56   11.108%   $240.6155   $240.62   $240.60   $240.60  
  Purchase #6 $153.54   7.548%   $165.1292   $165.13   $165.15   $165.10  
  Purchase #7 $29.57   5.683%   $31.2505   $31.25   $31.25   $31.30  
  7 purchase totals = $909.27       $996.6873   $996.69   $996.70   $996.70