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	$7.27	4.257%	$7.5795	$7.58	$7.60	$7.60
Purchase #2	$63.81	10.511%	$70.5171	$70.52	$70.50	$70.50
Purchase #3	$201.62	10.412%	$222.6127	$222.61	$222.60	$222.60
Purchase #4	$31.72	8.535%	$34.4273	$34.43	$34.45	$34.40
Purchase #5	$5.43	11.592%	$6.0594	$6.06	$6.05	$6.10
Purchase #6	$38.31	4.184%	$39.9129	$39.91	$39.90	$39.90
Purchase #7	$220.88	7.754%	$238.007	$238.01	$238.00	$238.00
7 purchase totals =	$569.04		$619.1159	$619.12	$619.10	$619.10