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	$31.85	4.587%	$33.311	$33.31	$33.30	$33.30
Purchase #2	$238.98	7.399%	$256.6621	$256.66	$256.65	$256.70
Purchase #3	$118.41	13.427%	$134.3089	$134.31	$134.30	$134.30
Purchase #4	$84.96	6.460%	$90.4484	$90.45	$90.45	$90.40
Purchase #5	$72.81	10.213%	$80.2461	$80.25	$80.25	$80.20
Purchase #6	$153.91	7.232%	$165.0408	$165.04	$165.05	$165.00
Purchase #7	$85.56	11.518%	$95.4148	$95.41	$95.40	$95.40
7 purchase totals =	$786.48		$855.4321	$855.43	$855.40	$855.30