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	$235.84	8.789%	$256.568	$256.57	$256.55	$256.60
Purchase #2	$60.97	13.259%	$69.054	$69.05	$69.05	$69.10
Purchase #3	$153.61	10.382%	$169.5578	$169.56	$169.55	$169.60
Purchase #4	$154.83	11.316%	$172.3506	$172.35	$172.35	$172.40
Purchase #5	$89.46	4.796%	$93.7505	$93.75	$93.75	$93.80
Purchase #6	$109.25	13.157%	$123.624	$123.62	$123.60	$123.60
Purchase #7	$35.55	13.216%	$40.2483	$40.25	$40.25	$40.20
7 purchase totals =	$839.51		$925.1532	$925.15	$925.10	$925.30