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	$18.60	12.113%	$20.853	$20.85	$20.85	$20.90
Purchase #2	$57.74	7.222%	$61.91	$61.91	$61.90	$61.90
Purchase #3	$88.84	6.303%	$94.4396	$94.44	$94.45	$94.40
Purchase #4	$45.36	3.276%	$46.846	$46.85	$46.85	$46.80
Purchase #5	$82.65	11.168%	$91.8804	$91.88	$91.90	$91.90
Purchase #6	$72.44	8.640%	$78.6988	$78.70	$78.70	$78.70
Purchase #7	$25.52	8.548%	$27.7014	$27.70	$27.70	$27.70
7 purchase totals =	$391.15		$422.3292	$422.33	$422.35	$422.30