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	$135.36	4.426%	$141.351	$141.35	$141.35	$141.40
Purchase #2	$239.44	4.760%	$250.8373	$250.84	$250.85	$250.80
Purchase #3	$77.37	11.752%	$86.4625	$86.46	$86.45	$86.50
Purchase #4	$234.42	8.307%	$253.8933	$253.89	$253.90	$253.90
Purchase #5	$183.78	8.407%	$199.2304	$199.23	$199.25	$199.20
Purchase #6	$12.95	3.382%	$13.388	$13.39	$13.40	$13.40
Purchase #7	$86.31	4.403%	$90.1102	$90.11	$90.10	$90.10
7 purchase totals =	$969.63		$1,035.2727	$1,035.27	$1,035.30	$1,035.30