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	$127.78	7.413%	$137.2523	$137.25	$137.25	$137.30
Purchase #2	$26.52	10.242%	$29.2362	$29.24	$29.25	$29.20
Purchase #3	$83.39	7.872%	$89.9545	$89.95	$89.95	$90.00
Purchase #4	$214.83	3.854%	$223.1095	$223.11	$223.10	$223.10
Purchase #5	$180.37	5.515%	$190.3174	$190.32	$190.30	$190.30
Purchase #6	$123.85	5.207%	$130.2989	$130.30	$130.30	$130.30
Purchase #7	$33.74	4.374%	$35.2158	$35.22	$35.20	$35.20
7 purchase totals =	$790.48		$835.3846	$835.39	$835.35	$835.40