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	$80.49	10.242%	$88.7338	$88.73	$88.75	$88.70
Purchase #2	$236.68	7.780%	$255.0937	$255.09	$255.10	$255.10
Purchase #3	$139.83	7.434%	$150.225	$150.23	$150.25	$150.20
Purchase #4	$189.64	6.817%	$202.5678	$202.57	$202.55	$202.60
Purchase #5	$177.72	10.438%	$196.2704	$196.27	$196.25	$196.30
Purchase #6	$29.85	12.536%	$33.592	$33.59	$33.60	$33.60
Purchase #7	$16.93	7.714%	$18.236	$18.24	$18.25	$18.20
7 purchase totals =	$871.14		$944.7187	$944.72	$944.75	$944.70