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	$43.88	4.189%	$45.7181	$45.72	$45.70	$45.70
Purchase #2	$171.37	4.171%	$178.5178	$178.52	$178.50	$178.50
Purchase #3	$120.33	6.791%	$128.5016	$128.50	$128.50	$128.50
Purchase #4	$64.80	10.216%	$71.42	$71.42	$71.40	$71.40
Purchase #5	$163.51	3.166%	$168.6867	$168.69	$168.70	$168.70
Purchase #6	$116.81	11.501%	$130.2443	$130.24	$130.25	$130.20
Purchase #7	$69.48	5.111%	$73.0311	$73.03	$73.05	$73.00
7 purchase totals =	$750.18		$796.1196	$796.12	$796.10	$796.00