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	$7.90	5.322%	$8.3204	$8.32	$8.30	$8.30
Purchase #2	$151.78	13.869%	$172.8304	$172.83	$172.85	$172.80
Purchase #3	$140.34	8.387%	$152.1103	$152.11	$152.10	$152.10
Purchase #4	$123.56	8.579%	$134.1602	$134.16	$134.15	$134.20
Purchase #5	$127.64	13.318%	$144.6391	$144.64	$144.65	$144.60
Purchase #6	$86.30	9.132%	$94.1809	$94.18	$94.20	$94.20
Purchase #7	$90.52	5.284%	$95.3031	$95.30	$95.30	$95.30
7 purchase totals =	$728.04		$801.5444	$801.54	$801.55	$801.50