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	$7.61	3.511%	$7.8772	$7.88	$7.90	$7.90
Purchase #2	$243.89	11.606%	$272.1959	$272.20	$272.20	$272.20
Purchase #3	$246.76	13.175%	$279.2706	$279.27	$279.25	$279.30
Purchase #4	$124.89	13.375%	$141.594	$141.59	$141.60	$141.60
Purchase #5	$139.84	10.360%	$154.3274	$154.33	$154.35	$154.30
Purchase #6	$66.99	5.802%	$70.8768	$70.88	$70.90	$70.90
Purchase #7	$235.74	10.201%	$259.7878	$259.79	$259.80	$259.80
7 purchase totals =	$1,065.72		$1,185.9297	$1,185.94	$1,186.00	$1,186.00