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	$50.76	7.853%	$54.7462	$54.75	$54.75	$54.70
Purchase #2	$96.29	8.272%	$104.2551	$104.26	$104.25	$104.30
Purchase #3	$52.69	12.398%	$59.2225	$59.22	$59.20	$59.20
Purchase #4	$247.41	12.851%	$279.2047	$279.20	$279.20	$279.20
Purchase #5	$224.56	7.308%	$240.9708	$240.97	$240.95	$241.00
Purchase #6	$28.87	5.848%	$30.5583	$30.56	$30.55	$30.60
Purchase #7	$53.25	11.319%	$59.2774	$59.28	$59.30	$59.30
7 purchase totals =	$753.83		$828.2350	$828.24	$828.20	$828.30