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	$86.59	7.316%	$92.9249	$92.92	$92.90	$92.90
Purchase #2	$158.30	9.467%	$173.2863	$173.29	$173.30	$173.30
Purchase #3	$79.91	8.578%	$86.7647	$86.76	$86.75	$86.80
Purchase #4	$28.48	12.514%	$32.044	$32.04	$32.05	$32.00
Purchase #5	$232.25	4.468%	$242.6269	$242.63	$242.65	$242.60
Purchase #6	$32.39	11.689%	$36.1761	$36.18	$36.20	$36.20
Purchase #7	$90.46	13.407%	$102.588	$102.59	$102.60	$102.60
7 purchase totals =	$708.38		$766.4109	$766.41	$766.45	$766.40