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	$60.74	6.756%	$64.8436	$64.84	$64.85	$64.80
Purchase #2	$36.50	5.488%	$38.5031	$38.50	$38.50	$38.50
Purchase #3	$249.66	12.371%	$280.5454	$280.55	$280.55	$280.50
Purchase #4	$25.45	10.669%	$28.1653	$28.17	$28.15	$28.20
Purchase #5	$219.32	4.251%	$228.6433	$228.64	$228.65	$228.60
Purchase #6	$83.59	6.764%	$89.244	$89.24	$89.25	$89.20
Purchase #7	$142.97	11.440%	$159.3258	$159.33	$159.35	$159.30
7 purchase totals =	$818.23		$889.2705	$889.27	$889.30	$889.10