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	$127.59	10.718%	$141.2651	$141.27	$141.25	$141.30
Purchase #2	$101.92	10.267%	$112.3841	$112.38	$112.40	$112.40
Purchase #3	$171.44	8.736%	$186.417	$186.42	$186.40	$186.40
Purchase #4	$10.37	12.591%	$11.6757	$11.68	$11.70	$11.70
Purchase #5	$155.62	6.365%	$165.5252	$165.53	$165.55	$165.50
Purchase #6	$39.28	3.764%	$40.7585	$40.76	$40.75	$40.80
Purchase #7	$32.26	5.214%	$33.942	$33.94	$33.95	$33.90
7 purchase totals =	$638.48		$691.9676	$691.98	$692.00	$692.00