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	$10.61	6.636%	$11.3141	$11.31	$11.30	$11.30
Purchase #2	$148.57	13.242%	$168.2436	$168.24	$168.25	$168.20
Purchase #3	$129.81	12.111%	$145.5313	$145.53	$145.55	$145.50
Purchase #4	$196.30	6.717%	$209.4855	$209.49	$209.50	$209.50
Purchase #5	$94.67	11.280%	$105.3488	$105.35	$105.35	$105.30
Purchase #6	$133.98	7.852%	$144.5001	$144.50	$144.50	$144.50
Purchase #7	$65.28	9.817%	$71.6885	$71.69	$71.70	$71.70
7 purchase totals =	$779.22		$856.1119	$856.11	$856.15	$856.00