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	$145.62	13.823%	$165.7491	$165.75	$165.75	$165.70
Purchase #2	$57.33	7.811%	$61.808	$61.81	$61.80	$61.80
Purchase #3	$53.54	12.672%	$60.3246	$60.32	$60.30	$60.30
Purchase #4	$80.28	4.144%	$83.6068	$83.61	$83.60	$83.60
Purchase #5	$161.67	8.771%	$175.8501	$175.85	$175.85	$175.90
Purchase #6	$94.76	9.402%	$103.6693	$103.67	$103.65	$103.70
Purchase #7	$122.80	12.290%	$137.8921	$137.89	$137.90	$137.90
7 purchase totals =	$716.00		$788.9000	$788.90	$788.85	$788.90