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	$39.50	4.550%	$41.2973	$41.30	$41.30	$41.30
Purchase #2	$53.25	11.113%	$59.1677	$59.17	$59.15	$59.20
Purchase #3	$196.44	7.599%	$211.3675	$211.37	$211.35	$211.40
Purchase #4	$154.31	11.596%	$172.2038	$172.20	$172.20	$172.20
Purchase #5	$181.59	10.332%	$200.3519	$200.35	$200.35	$200.40
Purchase #6	$52.37	9.316%	$57.2488	$57.25	$57.25	$57.20
Purchase #7	$36.25	3.585%	$37.5496	$37.55	$37.55	$37.50
7 purchase totals =	$713.71		$779.1866	$779.19	$779.15	$779.20