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	$39.37	6.407%	$41.8924	$41.89	$41.90	$41.90
Purchase #2	$56.27	8.777%	$61.2088	$61.21	$61.20	$61.20
Purchase #3	$79.84	3.716%	$82.8069	$82.81	$82.80	$82.80
Purchase #4	$111.66	4.164%	$116.3095	$116.31	$116.30	$116.30
Purchase #5	$165.93	11.323%	$184.7183	$184.72	$184.70	$184.70
Purchase #6	$115.95	12.134%	$130.0194	$130.02	$130.00	$130.00
Purchase #7	$135.88	8.531%	$147.4719	$147.47	$147.45	$147.50
7 purchase totals =	$704.90		$764.4272	$764.43	$764.35	$764.40