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	$245.49	13.760%	$279.2694	$279.27	$279.25	$279.30
Purchase #2	$146.37	9.803%	$160.7187	$160.72	$160.70	$160.70
Purchase #3	$97.32	8.178%	$105.2788	$105.28	$105.30	$105.30
Purchase #4	$95.99	11.364%	$106.8983	$106.90	$106.90	$106.90
Purchase #5	$209.89	9.514%	$229.8589	$229.86	$229.85	$229.90
Purchase #6	$77.33	10.502%	$85.4512	$85.45	$85.45	$85.50
Purchase #7	$152.48	8.400%	$165.2883	$165.29	$165.30	$165.30
7 purchase totals =	$1,024.87		$1,132.7636	$1,132.77	$1,132.75	$1,132.90