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	$20.61	6.202%	$21.8882	$21.89	$21.90	$21.90
Purchase #2	$198.91	6.543%	$211.9247	$211.92	$211.90	$211.90
Purchase #3	$154.83	12.290%	$173.8586	$173.86	$173.85	$173.90
Purchase #4	$76.81	8.614%	$83.4264	$83.43	$83.45	$83.40
Purchase #5	$38.68	13.165%	$43.7722	$43.77	$43.75	$43.80
Purchase #6	$231.81	13.439%	$262.9629	$262.96	$262.95	$263.00
Purchase #7	$191.30	4.172%	$199.281	$199.28	$199.30	$199.30
7 purchase totals =	$912.95		$997.1140	$997.11	$997.10	$997.20