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	$170.79	8.482%	$185.2764	$185.28	$185.30	$185.30
Purchase #2	$40.56	4.406%	$42.3471	$42.35	$42.35	$42.30
Purchase #3	$148.69	8.343%	$161.0952	$161.10	$161.10	$161.10
Purchase #4	$97.61	12.513%	$109.8239	$109.82	$109.80	$109.80
Purchase #5	$50.43	10.497%	$55.7236	$55.72	$55.70	$55.70
Purchase #6	$153.39	10.243%	$169.1017	$169.10	$169.10	$169.10
Purchase #7	$171.64	11.194%	$190.8534	$190.85	$190.85	$190.90
7 purchase totals =	$833.11		$914.2213	$914.22	$914.20	$914.20