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	$45.56	3.432%	$47.1236	$47.12	$47.10	$47.10
Purchase #2	$141.31	3.222%	$145.863	$145.86	$145.85	$145.90
Purchase #3	$137.40	13.753%	$156.2966	$156.30	$156.30	$156.30
Purchase #4	$93.51	8.361%	$101.3284	$101.33	$101.35	$101.30
Purchase #5	$201.80	10.478%	$222.9446	$222.94	$222.95	$222.90
Purchase #6	$147.42	3.655%	$152.8082	$152.81	$152.80	$152.80
Purchase #7	$42.66	9.196%	$46.583	$46.58	$46.60	$46.60
7 purchase totals =	$809.66		$872.9474	$872.94	$872.95	$872.90