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	$50.50	5.650%	$53.3533	$53.35	$53.35	$53.40
Purchase #2	$245.72	12.565%	$276.5947	$276.59	$276.60	$276.60
Purchase #3	$96.47	8.858%	$105.0153	$105.02	$105.00	$105.00
Purchase #4	$95.81	3.549%	$99.2103	$99.21	$99.20	$99.20
Purchase #5	$47.53	12.620%	$53.5283	$53.53	$53.55	$53.50
Purchase #6	$159.90	7.722%	$172.2475	$172.25	$172.25	$172.20
Purchase #7	$93.49	11.647%	$104.3788	$104.38	$104.40	$104.40
7 purchase totals =	$789.42		$864.3282	$864.33	$864.35	$864.30