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	$166.43	13.138%	$188.2956	$188.30	$188.30	$188.30
Purchase #2	$36.60	8.633%	$39.7597	$39.76	$39.75	$39.80
Purchase #3	$169.61	11.664%	$189.3933	$189.39	$189.40	$189.40
Purchase #4	$212.49	12.399%	$238.8366	$238.84	$238.85	$238.80
Purchase #5	$91.81	9.740%	$100.7523	$100.75	$100.75	$100.80
Purchase #6	$227.71	12.684%	$256.5927	$256.59	$256.60	$256.60
Purchase #7	$154.62	9.489%	$169.2919	$169.29	$169.30	$169.30
7 purchase totals =	$1,059.27		$1,182.9221	$1,182.92	$1,182.95	$1,183.00