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	$211.62	13.498%	$240.1845	$240.18	$240.20	$240.20
Purchase #2	$122.68	4.360%	$128.0288	$128.03	$128.05	$128.00
Purchase #3	$35.47	4.648%	$37.1186	$37.12	$37.10	$37.10
Purchase #4	$86.74	10.466%	$95.8182	$95.82	$95.80	$95.80
Purchase #5	$28.81	12.748%	$32.4827	$32.48	$32.50	$32.50
Purchase #6	$135.83	12.217%	$152.4244	$152.42	$152.40	$152.40
Purchase #7	$94.40	12.575%	$106.2708	$106.27	$106.25	$106.30
7 purchase totals =	$715.55		$792.3280	$792.32	$792.30	$792.30