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 $52.77   6.783%   $56.3494   $56.35   $56.35   $56.30  
  Purchase #2 $79.25   13.434%   $89.8964   $89.90   $89.90   $89.90  
  Purchase #3 $150.77   10.809%   $167.0667   $167.07   $167.05   $167.10  
  Purchase #4 $56.96   13.457%   $64.6251   $64.63   $64.65   $64.60  
  Purchase #5 $226.49   7.117%   $242.6093   $242.61   $242.60   $242.60  
  Purchase #6 $84.60   12.351%   $95.0489   $95.05   $95.05   $95.00  
  Purchase #7 $226.88   9.641%   $248.7535   $248.75   $248.75   $248.80  
  7 purchase totals = $877.72       $964.3493   $964.36   $964.35   $964.30