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	$81.77	11.624%	$91.2749	$91.27	$91.25	$91.30
Purchase #2	$106.62	4.222%	$111.1215	$111.12	$111.10	$111.10
Purchase #3	$179.88	5.217%	$189.2643	$189.26	$189.25	$189.30
Purchase #4	$83.26	8.206%	$90.0923	$90.09	$90.10	$90.10
Purchase #5	$85.36	6.403%	$90.8256	$90.83	$90.85	$90.80
Purchase #6	$121.73	11.631%	$135.8884	$135.89	$135.90	$135.90
Purchase #7	$106.82	4.373%	$111.4912	$111.49	$111.50	$111.50
7 purchase totals =	$765.44		$819.9582	$819.95	$819.95	$820.00