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	$67.27	7.330%	$72.2009	$72.20	$72.20	$72.20
Purchase #2	$57.28	12.362%	$64.361	$64.36	$64.35	$64.40
Purchase #3	$32.31	10.698%	$35.7665	$35.77	$35.75	$35.80
Purchase #4	$161.91	8.619%	$175.865	$175.87	$175.85	$175.90
Purchase #5	$49.74	12.605%	$56.0097	$56.01	$56.00	$56.00
Purchase #6	$18.72	9.428%	$20.4849	$20.48	$20.50	$20.50
Purchase #7	$80.39	12.795%	$90.6759	$90.68	$90.70	$90.70
7 purchase totals =	$467.62		$515.3639	$515.37	$515.35	$515.50