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	$225.70	3.518%	$233.6401	$233.64	$233.65	$233.60
Purchase #2	$154.72	9.130%	$168.8459	$168.85	$168.85	$168.80
Purchase #3	$179.93	5.627%	$190.0547	$190.05	$190.05	$190.10
Purchase #4	$140.84	4.255%	$146.8327	$146.83	$146.85	$146.80
Purchase #5	$39.44	7.667%	$42.4639	$42.46	$42.45	$42.50
Purchase #6	$236.48	6.523%	$251.9056	$251.91	$251.90	$251.90
Purchase #7	$209.32	9.549%	$229.308	$229.31	$229.30	$229.30
7 purchase totals =	$1,186.43		$1,263.0509	$1,263.05	$1,263.05	$1,263.00