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	$35.48	6.454%	$37.7699	$37.77	$37.75	$37.80
Purchase #2	$134.60	13.443%	$152.6943	$152.69	$152.70	$152.70
Purchase #3	$230.84	5.561%	$243.677	$243.68	$243.70	$243.70
Purchase #4	$10.28	6.217%	$10.9191	$10.92	$10.90	$10.90
Purchase #5	$89.74	6.658%	$95.7149	$95.71	$95.70	$95.70
Purchase #6	$124.98	9.147%	$136.4119	$136.41	$136.40	$136.40
Purchase #7	$215.94	3.275%	$223.012	$223.01	$223.00	$223.00
7 purchase totals =	$841.86		$900.1991	$900.19	$900.15	$900.20