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	$63.65	6.487%	$67.779	$67.78	$67.80	$67.80
Purchase #2	$85.93	4.265%	$89.5949	$89.59	$89.60	$89.60
Purchase #3	$75.27	7.568%	$80.9664	$80.97	$80.95	$81.00
Purchase #4	$159.32	12.454%	$179.1617	$179.16	$179.15	$179.20
Purchase #5	$170.45	7.388%	$183.0428	$183.04	$183.05	$183.00
Purchase #6	$33.50	10.575%	$37.0426	$37.04	$37.05	$37.00
Purchase #7	$170.77	10.516%	$188.7282	$188.73	$188.75	$188.70
7 purchase totals =	$758.89		$826.3156	$826.31	$826.35	$826.30