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 $217.43   11.181%   $241.7408   $241.74   $241.75   $241.70  
  Purchase #2 $182.74   13.292%   $207.0298   $207.03   $207.05   $207.00  
  Purchase #3 $202.60   9.187%   $221.2129   $221.21   $221.20   $221.20  
  Purchase #4 $11.36   13.565%   $12.901   $12.90   $12.90   $12.90  
  Purchase #5 $177.30   8.539%   $192.4396   $192.44   $192.45   $192.40  
  Purchase #6 $208.80   10.572%   $230.8743   $230.87   $230.85   $230.90  
  Purchase #7 $161.37   4.811%   $169.1335   $169.13   $169.15   $169.10  
  7 purchase totals = $1,161.60       $1,275.3319   $1,275.32   $1,275.35   $1,275.20