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	$48.67	11.503%	$54.2685	$54.27	$54.25	$54.30
Purchase #2	$18.98	6.717%	$20.2549	$20.25	$20.25	$20.30
Purchase #3	$169.86	6.870%	$181.5294	$181.53	$181.55	$181.50
Purchase #4	$115.91	11.211%	$128.9047	$128.90	$128.90	$128.90
Purchase #5	$210.34	13.488%	$238.7107	$238.71	$238.70	$238.70
Purchase #6	$200.35	10.504%	$221.3948	$221.39	$221.40	$221.40
Purchase #7	$42.91	3.197%	$44.2818	$44.28	$44.30	$44.30
7 purchase totals =	$807.02		$889.3448	$889.33	$889.35	$889.40