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	$37.81	12.233%	$42.4353	$42.44	$42.45	$42.40
Purchase #2	$76.45	3.230%	$78.9193	$78.92	$78.90	$78.90
Purchase #3	$95.40	9.387%	$104.3552	$104.36	$104.35	$104.40
Purchase #4	$136.42	5.861%	$144.4156	$144.42	$144.40	$144.40
Purchase #5	$159.56	6.756%	$170.3399	$170.34	$170.35	$170.30
Purchase #6	$203.30	12.251%	$228.2063	$228.21	$228.20	$228.20
Purchase #7	$128.41	13.184%	$145.3396	$145.34	$145.35	$145.30
7 purchase totals =	$837.35		$914.0112	$914.03	$914.00	$913.90