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	$37.38	6.369%	$39.7607	$39.76	$39.75	$39.80
Purchase #2	$43.66	4.614%	$45.6745	$45.67	$45.65	$45.70
Purchase #3	$57.57	11.433%	$64.152	$64.15	$64.15	$64.20
Purchase #4	$155.65	8.261%	$168.5082	$168.51	$168.50	$168.50
Purchase #5	$242.52	13.228%	$274.6005	$274.60	$274.60	$274.60
Purchase #6	$59.97	12.481%	$67.4549	$67.45	$67.45	$67.50
Purchase #7	$186.58	3.236%	$192.6177	$192.62	$192.60	$192.60
7 purchase totals =	$783.33		$852.7685	$852.76	$852.70	$852.90