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	$76.59	12.848%	$86.4303	$86.43	$86.45	$86.40
Purchase #2	$118.46	7.612%	$127.4772	$127.48	$127.50	$127.50
Purchase #3	$77.78	13.824%	$88.5323	$88.53	$88.55	$88.50
Purchase #4	$196.34	3.474%	$203.1609	$203.16	$203.15	$203.20
Purchase #5	$41.45	10.190%	$45.6738	$45.67	$45.65	$45.70
Purchase #6	$21.98	4.296%	$22.9243	$22.92	$22.90	$22.90
Purchase #7	$94.71	12.495%	$106.544	$106.54	$106.55	$106.50
7 purchase totals =	$627.31		$680.7428	$680.73	$680.75	$680.70