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	$249.42	8.598%	$270.8651	$270.87	$270.85	$270.90
Purchase #2	$100.47	5.314%	$105.809	$105.81	$105.80	$105.80
Purchase #3	$105.99	3.152%	$109.3308	$109.33	$109.35	$109.30
Purchase #4	$113.71	4.688%	$119.0407	$119.04	$119.05	$119.00
Purchase #5	$80.92	11.378%	$90.1271	$90.13	$90.15	$90.10
Purchase #6	$140.65	4.461%	$146.9244	$146.92	$146.90	$146.90
Purchase #7	$189.51	11.345%	$211.0099	$211.01	$211.00	$211.00
7 purchase totals =	$980.67		$1,053.1070	$1,053.11	$1,053.10	$1,053.00