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	$144.32	11.237%	$160.5372	$160.54	$160.55	$160.50
Purchase #2	$115.89	7.451%	$124.525	$124.53	$124.55	$124.50
Purchase #3	$39.36	8.424%	$42.6757	$42.68	$42.70	$42.70
Purchase #4	$53.48	10.668%	$59.1852	$59.19	$59.20	$59.20
Purchase #5	$106.71	4.790%	$111.8214	$111.82	$111.80	$111.80
Purchase #6	$105.92	4.135%	$110.2998	$110.30	$110.30	$110.30
Purchase #7	$181.87	13.457%	$206.3442	$206.34	$206.35	$206.30
7 purchase totals =	$747.55		$815.3885	$815.40	$815.45	$815.30