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	$29.77	12.314%	$33.4359	$33.44	$33.45	$33.40
Purchase #2	$98.61	10.298%	$108.7649	$108.76	$108.75	$108.80
Purchase #3	$167.52	7.130%	$179.4642	$179.46	$179.45	$179.50
Purchase #4	$37.43	13.640%	$42.5355	$42.54	$42.55	$42.50
Purchase #5	$67.82	6.642%	$72.3246	$72.32	$72.30	$72.30
Purchase #6	$237.98	9.705%	$261.076	$261.08	$261.10	$261.10
Purchase #7	$152.50	8.233%	$165.0553	$165.06	$165.05	$165.10
7 purchase totals =	$791.63		$862.6564	$862.66	$862.65	$862.70