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	$146.33	12.844%	$165.1246	$165.12	$165.10	$165.10
Purchase #2	$149.85	9.837%	$164.5907	$164.59	$164.60	$164.60
Purchase #3	$89.39	8.140%	$96.6663	$96.67	$96.65	$96.70
Purchase #4	$160.29	12.624%	$180.525	$180.53	$180.55	$180.50
Purchase #5	$59.64	9.667%	$65.4054	$65.41	$65.40	$65.40
Purchase #6	$201.63	10.294%	$222.3858	$222.39	$222.40	$222.40
Purchase #7	$59.52	4.681%	$62.3061	$62.31	$62.30	$62.30
7 purchase totals =	$866.65		$957.0039	$957.02	$957.00	$957.00