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	$110.80	12.163%	$124.2766	$124.28	$124.30	$124.30
Purchase #2	$158.97	6.487%	$169.2824	$169.28	$169.30	$169.30
Purchase #3	$117.30	12.363%	$131.8018	$131.80	$131.80	$131.80
Purchase #4	$184.40	8.105%	$199.3456	$199.35	$199.35	$199.30
Purchase #5	$214.42	12.345%	$240.8901	$240.89	$240.90	$240.90
Purchase #6	$63.45	12.377%	$71.3032	$71.30	$71.30	$71.30
Purchase #7	$205.35	8.859%	$223.542	$223.54	$223.55	$223.50
7 purchase totals =	$1,054.69		$1,160.4417	$1,160.44	$1,160.50	$1,160.40