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	$217.35	11.364%	$242.0497	$242.05	$242.05	$242.00
Purchase #2	$124.73	12.346%	$140.1292	$140.13	$140.15	$140.10
Purchase #3	$80.66	11.449%	$89.8948	$89.89	$89.90	$89.90
Purchase #4	$117.64	9.489%	$128.8029	$128.80	$128.80	$128.80
Purchase #5	$34.81	9.811%	$38.2252	$38.23	$38.25	$38.20
Purchase #6	$10.49	12.714%	$11.8237	$11.82	$11.80	$11.80
Purchase #7	$101.50	3.177%	$104.7247	$104.72	$104.70	$104.70
7 purchase totals =	$687.18		$755.6502	$755.64	$755.65	$755.50