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	$128.89	8.673%	$140.0686	$140.07	$140.05	$140.10
Purchase #2	$249.58	8.437%	$270.6371	$270.64	$270.65	$270.60
Purchase #3	$39.33	11.437%	$43.8282	$43.83	$43.85	$43.80
Purchase #4	$218.29	7.250%	$234.116	$234.12	$234.10	$234.10
Purchase #5	$91.82	9.195%	$100.2628	$100.26	$100.25	$100.30
Purchase #6	$73.71	6.580%	$78.5601	$78.56	$78.55	$78.60
Purchase #7	$9.46	12.487%	$10.6413	$10.64	$10.65	$10.60
7 purchase totals =	$811.08		$878.1141	$878.12	$878.10	$878.10