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	$84.82	6.770%	$90.5623	$90.56	$90.55	$90.60
Purchase #2	$78.30	4.570%	$81.8783	$81.88	$81.90	$81.90
Purchase #3	$9.97	5.388%	$10.5072	$10.51	$10.50	$10.50
Purchase #4	$54.92	11.392%	$61.1765	$61.18	$61.20	$61.20
Purchase #5	$103.54	6.407%	$110.1738	$110.17	$110.15	$110.20
Purchase #6	$250.25	13.119%	$283.0803	$283.08	$283.10	$283.10
Purchase #7	$42.67	5.142%	$44.8641	$44.86	$44.85	$44.90
7 purchase totals =	$624.47		$682.2425	$682.24	$682.25	$682.40