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	$96.73	9.400%	$105.8226	$105.82	$105.80	$105.80
Purchase #2	$96.77	10.222%	$106.6618	$106.66	$106.65	$106.70
Purchase #3	$174.26	8.629%	$189.2969	$189.30	$189.30	$189.30
Purchase #4	$37.51	12.527%	$42.2089	$42.21	$42.20	$42.20
Purchase #5	$112.81	13.448%	$127.9807	$127.98	$128.00	$128.00
Purchase #6	$32.51	9.171%	$35.4915	$35.49	$35.50	$35.50
Purchase #7	$45.26	12.439%	$50.8899	$50.89	$50.90	$50.90
7 purchase totals =	$595.85		$658.3523	$658.35	$658.35	$658.40