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	$165.87	13.586%	$188.4051	$188.41	$188.40	$188.40
Purchase #2	$102.67	6.737%	$109.5869	$109.59	$109.60	$109.60
Purchase #3	$216.67	11.690%	$241.9987	$242.00	$242.00	$242.00
Purchase #4	$100.35	6.319%	$106.6911	$106.69	$106.70	$106.70
Purchase #5	$145.46	9.874%	$159.8227	$159.82	$159.80	$159.80
Purchase #6	$70.40	3.334%	$72.7471	$72.75	$72.75	$72.70
Purchase #7	$56.96	7.720%	$61.3573	$61.36	$61.35	$61.40
7 purchase totals =	$858.38		$940.6089	$940.62	$940.60	$940.60