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 $168.91   6.854%   $180.4871   $180.49   $180.50   $180.50  
  Purchase #2 $128.44   6.696%   $137.0403   $137.04   $137.05   $137.00  
  Purchase #3 $61.28   4.553%   $64.0701   $64.07   $64.05   $64.10  
  Purchase #4 $195.55   5.365%   $206.0413   $206.04   $206.05   $206.00  
  Purchase #5 $58.26   13.573%   $66.1676   $66.17   $66.15   $66.20  
  Purchase #6 $151.26   13.571%   $171.7875   $171.79   $171.80   $171.80  
  Purchase #7 $175.33   13.594%   $199.1644   $199.16   $199.15   $199.20  
  7 purchase totals = $939.03       $1,024.7583   $1,024.76   $1,024.75   $1,024.80