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	$40.25	6.425%	$42.8361	$42.84	$42.85	$42.80
Purchase #2	$148.60	12.243%	$166.7931	$166.79	$166.80	$166.80
Purchase #3	$171.46	5.399%	$180.7171	$180.72	$180.70	$180.70
Purchase #4	$186.42	5.408%	$196.5016	$196.50	$196.50	$196.50
Purchase #5	$91.89	9.744%	$100.8438	$100.84	$100.85	$100.80
Purchase #6	$92.42	10.707%	$102.3154	$102.32	$102.30	$102.30
Purchase #7	$192.74	5.125%	$202.6179	$202.62	$202.60	$202.60
7 purchase totals =	$923.78		$992.6250	$992.63	$992.60	$992.50