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	$158.90	8.732%	$172.7751	$172.78	$172.80	$172.80
Purchase #2	$162.57	13.813%	$185.0258	$185.03	$185.05	$185.00
Purchase #3	$147.95	5.313%	$155.8106	$155.81	$155.80	$155.80
Purchase #4	$189.34	5.490%	$199.7348	$199.73	$199.75	$199.70
Purchase #5	$141.86	6.207%	$150.6653	$150.67	$150.65	$150.70
Purchase #6	$188.59	5.116%	$198.2383	$198.24	$198.25	$198.20
Purchase #7	$40.50	12.379%	$45.5135	$45.51	$45.50	$45.50
7 purchase totals =	$1,029.71		$1,107.7634	$1,107.77	$1,107.80	$1,107.70