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	$21.38	12.481%	$24.0484	$24.05	$24.05	$24.00
Purchase #2	$125.79	12.467%	$141.4722	$141.47	$141.45	$141.50
Purchase #3	$217.93	9.362%	$238.3326	$238.33	$238.35	$238.30
Purchase #4	$48.61	12.388%	$54.6318	$54.63	$54.65	$54.60
Purchase #5	$221.55	9.518%	$242.6371	$242.64	$242.65	$242.60
Purchase #6	$99.81	9.581%	$109.3728	$109.37	$109.35	$109.40
Purchase #7	$209.72	6.280%	$222.8904	$222.89	$222.90	$222.90
7 purchase totals =	$944.79		$1,033.3853	$1,033.38	$1,033.40	$1,033.30