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	$110.30	6.234%	$117.1761	$117.18	$117.20	$117.20
Purchase #2	$79.89	7.157%	$85.6077	$85.61	$85.60	$85.60
Purchase #3	$201.35	11.258%	$224.018	$224.02	$224.00	$224.00
Purchase #4	$155.83	10.233%	$171.7761	$171.78	$171.80	$171.80
Purchase #5	$245.72	6.186%	$260.9202	$260.92	$260.90	$260.90
Purchase #6	$192.37	12.570%	$216.5509	$216.55	$216.55	$216.60
Purchase #7	$180.92	8.544%	$196.3778	$196.38	$196.40	$196.40
7 purchase totals =	$1,166.38		$1,272.4268	$1,272.44	$1,272.45	$1,272.50