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 $167.96   10.518%   $185.626   $185.63   $185.65   $185.60  
  Purchase #2 $233.53   11.341%   $260.0146   $260.01   $260.00   $260.00  
  Purchase #3 $242.43   8.805%   $263.776   $263.78   $263.80   $263.80  
  Purchase #4 $168.26   8.448%   $182.4746   $182.47   $182.45   $182.50  
  Purchase #5 $50.55   11.834%   $56.5321   $56.53   $56.55   $56.50  
  Purchase #6 $135.43   8.748%   $147.2774   $147.28   $147.30   $147.30  
  Purchase #7 $195.95   6.294%   $208.2831   $208.28   $208.30   $208.30  
  7 purchase totals = $1,194.11       $1,303.9838   $1,303.98   $1,304.05   $1,304.00