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	$155.40	11.670%	$173.5352	$173.54	$173.55	$173.50
Purchase #2	$67.98	12.155%	$76.243	$76.24	$76.25	$76.20
Purchase #3	$62.76	3.281%	$64.8192	$64.82	$64.80	$64.80
Purchase #4	$40.41	4.741%	$42.3258	$42.33	$42.35	$42.30
Purchase #5	$40.63	7.313%	$43.6013	$43.60	$43.60	$43.60
Purchase #6	$58.98	5.157%	$62.0216	$62.02	$62.00	$62.00
Purchase #7	$169.77	8.351%	$183.9475	$183.95	$183.95	$183.90
7 purchase totals =	$595.93		$646.4936	$646.50	$646.50	$646.30