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	$38.75	9.401%	$42.3929	$42.39	$42.40	$42.40
Purchase #2	$224.56	6.118%	$238.2986	$238.30	$238.30	$238.30
Purchase #3	$39.82	9.715%	$43.6885	$43.69	$43.70	$43.70
Purchase #4	$161.91	6.531%	$172.4843	$172.48	$172.50	$172.50
Purchase #5	$51.99	12.567%	$58.5236	$58.52	$58.50	$58.50
Purchase #6	$83.71	11.686%	$93.4924	$93.49	$93.50	$93.50
Purchase #7	$210.90	6.105%	$223.7754	$223.78	$223.80	$223.80
7 purchase totals =	$811.64		$872.6557	$872.65	$872.70	$872.70