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 $242.84   10.201%   $267.6121   $267.61   $267.60   $267.60  
  Purchase #2 $9.60   7.276%   $10.2985   $10.30   $10.30   $10.30  
  Purchase #3 $184.73   4.207%   $192.5016   $192.50   $192.50   $192.50  
  Purchase #4 $25.44   7.472%   $27.3409   $27.34   $27.35   $27.30  
  Purchase #5 $242.62   3.150%   $250.2625   $250.26   $250.25   $250.30  
  Purchase #6 $220.75   11.186%   $245.4431   $245.44   $245.45   $245.40  
  Purchase #7 $61.35   5.482%   $64.7132   $64.71   $64.70   $64.70  
  7 purchase totals = $987.33       $1,058.1719   $1,058.16   $1,058.15   $1,058.10