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	$164.57	11.760%	$183.9234	$183.92	$183.90	$183.90
Purchase #2	$29.87	7.314%	$32.0547	$32.05	$32.05	$32.10
Purchase #3	$124.85	6.728%	$133.2499	$133.25	$133.25	$133.20
Purchase #4	$211.63	12.596%	$238.2869	$238.29	$238.30	$238.30
Purchase #5	$128.29	7.517%	$137.9336	$137.93	$137.95	$137.90
Purchase #6	$52.54	4.711%	$55.0152	$55.02	$55.00	$55.00
Purchase #7	$109.42	12.447%	$123.0395	$123.04	$123.05	$123.00
7 purchase totals =	$821.17		$903.5032	$903.50	$903.50	$903.40