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	$30.40	10.566%	$33.6121	$33.61	$33.60	$33.60
Purchase #2	$206.46	10.251%	$227.6242	$227.62	$227.60	$227.60
Purchase #3	$175.48	11.573%	$195.7883	$195.79	$195.80	$195.80
Purchase #4	$158.25	7.375%	$169.9209	$169.92	$169.90	$169.90
Purchase #5	$32.85	7.859%	$35.4317	$35.43	$35.45	$35.40
Purchase #6	$83.70	6.461%	$89.1079	$89.11	$89.10	$89.10
Purchase #7	$129.78	8.307%	$140.5608	$140.56	$140.55	$140.60
7 purchase totals =	$816.92		$892.0459	$892.04	$892.00	$892.00