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	$234.98	3.467%	$243.1268	$243.13	$243.15	$243.10
Purchase #2	$23.72	9.315%	$25.9295	$25.93	$25.95	$25.90
Purchase #3	$18.35	12.246%	$20.5971	$20.60	$20.60	$20.60
Purchase #4	$169.81	6.731%	$181.2399	$181.24	$181.25	$181.20
Purchase #5	$78.82	5.591%	$83.2268	$83.23	$83.25	$83.20
Purchase #6	$89.70	10.792%	$99.3804	$99.38	$99.40	$99.40
Purchase #7	$202.89	10.242%	$223.67	$223.67	$223.65	$223.70
7 purchase totals =	$818.27		$877.1705	$877.18	$877.25	$877.10