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	$74.51	10.248%	$82.1458	$82.15	$82.15	$82.10
Purchase #2	$118.94	3.342%	$122.915	$122.92	$122.90	$122.90
Purchase #3	$85.42	10.648%	$94.5155	$94.52	$94.50	$94.50
Purchase #4	$78.52	3.560%	$81.3153	$81.32	$81.30	$81.30
Purchase #5	$215.44	13.511%	$244.5481	$244.55	$244.55	$244.50
Purchase #6	$44.31	3.383%	$45.809	$45.81	$45.80	$45.80
Purchase #7	$75.72	3.330%	$78.2415	$78.24	$78.25	$78.20
7 purchase totals =	$692.86		$749.4902	$749.51	$749.45	$749.30