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	$141.89	10.281%	$156.4777	$156.48	$156.50	$156.50
Purchase #2	$180.43	5.816%	$190.9238	$190.92	$190.90	$190.90
Purchase #3	$96.29	12.452%	$108.28	$108.28	$108.30	$108.30
Purchase #4	$229.77	6.729%	$245.2312	$245.23	$245.25	$245.20
Purchase #5	$73.78	9.489%	$80.781	$80.78	$80.80	$80.80
Purchase #6	$98.99	5.373%	$104.3087	$104.31	$104.30	$104.30
Purchase #7	$18.79	8.756%	$20.4353	$20.44	$20.45	$20.40
7 purchase totals =	$839.94		$906.4377	$906.44	$906.50	$906.40