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	$109.27	13.405%	$123.9176	$123.92	$123.90	$123.90
Purchase #2	$14.69	7.753%	$15.8289	$15.83	$15.85	$15.80
Purchase #3	$231.48	3.272%	$239.054	$239.05	$239.05	$239.10
Purchase #4	$143.80	5.664%	$151.9448	$151.94	$151.95	$151.90
Purchase #5	$117.43	9.690%	$128.809	$128.81	$128.80	$128.80
Purchase #6	$143.56	8.675%	$156.0138	$156.01	$156.00	$156.00
Purchase #7	$229.89	3.743%	$238.4948	$238.49	$238.50	$238.50
7 purchase totals =	$990.12		$1,054.0629	$1,054.05	$1,054.05	$1,054.00