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	$91.28	13.155%	$103.2879	$103.29	$103.30	$103.30
Purchase #2	$54.66	12.110%	$61.2793	$61.28	$61.30	$61.30
Purchase #3	$36.83	13.185%	$41.686	$41.69	$41.70	$41.70
Purchase #4	$191.56	7.679%	$206.2699	$206.27	$206.25	$206.30
Purchase #5	$90.96	9.370%	$99.483	$99.48	$99.50	$99.50
Purchase #6	$217.93	13.772%	$247.9433	$247.94	$247.95	$247.90
Purchase #7	$185.29	3.780%	$192.294	$192.29	$192.30	$192.30
7 purchase totals =	$868.51		$952.2434	$952.24	$952.30	$952.30