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	$37.54	3.586%	$38.8862	$38.89	$38.90	$38.90
Purchase #2	$60.82	10.220%	$67.0358	$67.04	$67.05	$67.00
Purchase #3	$145.44	4.446%	$151.9063	$151.91	$151.90	$151.90
Purchase #4	$243.55	12.234%	$273.3459	$273.35	$273.35	$273.30
Purchase #5	$214.31	11.660%	$239.2985	$239.30	$239.30	$239.30
Purchase #6	$228.37	4.143%	$237.8314	$237.83	$237.85	$237.80
Purchase #7	$149.93	6.642%	$159.8884	$159.89	$159.90	$159.90
7 purchase totals =	$1,079.96		$1,168.1925	$1,168.21	$1,168.25	$1,168.10