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	$83.88	6.634%	$89.4446	$89.44	$89.45	$89.40
Purchase #2	$60.73	5.587%	$64.123	$64.12	$64.10	$64.10
Purchase #3	$241.61	11.118%	$268.4722	$268.47	$268.45	$268.50
Purchase #4	$56.89	9.606%	$62.3549	$62.35	$62.35	$62.40
Purchase #5	$171.44	5.488%	$180.8486	$180.85	$180.85	$180.80
Purchase #6	$234.61	8.843%	$255.3566	$255.36	$255.35	$255.40
Purchase #7	$70.44	9.566%	$77.1783	$77.18	$77.20	$77.20
7 purchase totals =	$919.60		$997.7782	$997.77	$997.75	$997.80