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	$231.31	7.456%	$248.5565	$248.56	$248.55	$248.60
Purchase #2	$135.90	12.128%	$152.382	$152.38	$152.40	$152.40
Purchase #3	$171.70	9.872%	$188.6502	$188.65	$188.65	$188.70
Purchase #4	$18.30	10.748%	$20.2669	$20.27	$20.25	$20.30
Purchase #5	$145.68	9.556%	$159.6012	$159.60	$159.60	$159.60
Purchase #6	$80.57	12.590%	$90.7138	$90.71	$90.70	$90.70
Purchase #7	$170.90	8.674%	$185.7239	$185.72	$185.70	$185.70
7 purchase totals =	$954.36		$1,045.8945	$1,045.89	$1,045.85	$1,046.00