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	$130.94	11.812%	$146.4066	$146.41	$146.40	$146.40
Purchase #2	$70.79	11.565%	$78.9769	$78.98	$79.00	$79.00
Purchase #3	$220.57	5.586%	$232.891	$232.89	$232.90	$232.90
Purchase #4	$107.69	9.440%	$117.8559	$117.86	$117.85	$117.90
Purchase #5	$10.39	4.155%	$10.8217	$10.82	$10.80	$10.80
Purchase #6	$37.69	3.417%	$38.9779	$38.98	$39.00	$39.00
Purchase #7	$144.81	6.561%	$154.311	$154.31	$154.30	$154.30
7 purchase totals =	$722.88		$780.2410	$780.25	$780.25	$780.30