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	$77.85	13.674%	$88.4952	$88.50	$88.50	$88.50
Purchase #2	$94.82	11.117%	$105.3611	$105.36	$105.35	$105.40
Purchase #3	$123.96	12.320%	$139.2319	$139.23	$139.25	$139.20
Purchase #4	$152.78	11.150%	$169.815	$169.82	$169.80	$169.80
Purchase #5	$161.30	5.698%	$170.4909	$170.49	$170.50	$170.50
Purchase #6	$211.55	11.714%	$236.331	$236.33	$236.35	$236.30
Purchase #7	$35.69	11.171%	$39.6769	$39.68	$39.70	$39.70
7 purchase totals =	$857.95		$949.4020	$949.41	$949.45	$949.40