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 $101.71   12.120%   $114.0373   $114.04   $114.05   $114.00  
  Purchase #2 $167.91   5.346%   $176.8865   $176.89   $176.90   $176.90  
  Purchase #3 $29.88   9.572%   $32.7401   $32.74   $32.75   $32.70  
  Purchase #4 $116.67   7.120%   $124.9769   $124.98   $125.00   $125.00  
  Purchase #5 $15.34   5.341%   $16.1593   $16.16   $16.15   $16.20  
  Purchase #6 $216.30   13.135%   $244.711   $244.71   $244.70   $244.70  
  Purchase #7 $177.53   4.815%   $186.0781   $186.08   $186.10   $186.10  
  7 purchase totals = $825.34       $895.5892   $895.60   $895.65   $895.60