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	$75.47	12.797%	$85.1279	$85.13	$85.15	$85.10
Purchase #2	$79.81	3.784%	$82.83	$82.83	$82.85	$82.80
Purchase #3	$144.77	11.151%	$160.9133	$160.91	$160.90	$160.90
Purchase #4	$169.41	11.605%	$189.07	$189.07	$189.05	$189.10
Purchase #5	$243.50	4.187%	$253.6953	$253.70	$253.70	$253.70
Purchase #6	$7.29	7.253%	$7.8187	$7.82	$7.80	$7.80
Purchase #7	$242.52	11.772%	$271.0695	$271.07	$271.05	$271.10
7 purchase totals =	$962.77		$1,050.5247	$1,050.53	$1,050.50	$1,050.50