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	$72.30	3.635%	$74.9281	$74.93	$74.95	$74.90
Purchase #2	$39.50	7.121%	$42.3128	$42.31	$42.30	$42.30
Purchase #3	$64.52	5.120%	$67.8234	$67.82	$67.80	$67.80
Purchase #4	$161.45	12.579%	$181.7588	$181.76	$181.75	$181.80
Purchase #5	$206.29	11.128%	$229.246	$229.25	$229.25	$229.20
Purchase #6	$227.77	3.289%	$235.2614	$235.26	$235.25	$235.30
Purchase #7	$152.51	10.496%	$168.5174	$168.52	$168.50	$168.50
7 purchase totals =	$924.34		$999.8479	$999.85	$999.80	$999.80