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 $96.63   13.575%   $109.7475   $109.75   $109.75   $109.70  
  Purchase #2 $210.86   12.764%   $237.7742   $237.77   $237.75   $237.80  
  Purchase #3 $16.84   3.483%   $17.4265   $17.43   $17.45   $17.40  
  Purchase #4 $240.87   4.828%   $252.4992   $252.50   $252.50   $252.50  
  Purchase #5 $136.82   11.110%   $152.0207   $152.02   $152.00   $152.00  
  Purchase #6 $50.96   12.812%   $57.489   $57.49   $57.50   $57.50  
  Purchase #7 $203.99   8.501%   $221.3312   $221.33   $221.35   $221.30  
  7 purchase totals = $956.97       $1,048.2883   $1,048.29   $1,048.30   $1,048.20