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	$238.51	13.783%	$271.3838	$271.38	$271.40	$271.40
Purchase #2	$80.28	12.820%	$90.5719	$90.57	$90.55	$90.60
Purchase #3	$95.92	10.622%	$106.1086	$106.11	$106.10	$106.10
Purchase #4	$204.43	7.269%	$219.29	$219.29	$219.30	$219.30
Purchase #5	$164.56	12.690%	$185.4427	$185.44	$185.45	$185.40
Purchase #6	$50.31	5.540%	$53.0972	$53.10	$53.10	$53.10
Purchase #7	$201.59	3.245%	$208.1316	$208.13	$208.15	$208.10
7 purchase totals =	$1,035.60		$1,134.0258	$1,134.02	$1,134.05	$1,134.00