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	$127.80	4.170%	$133.1293	$133.13	$133.15	$133.10
Purchase #2	$249.46	5.786%	$263.8938	$263.89	$263.90	$263.90
Purchase #3	$241.93	5.820%	$256.0103	$256.01	$256.00	$256.00
Purchase #4	$170.89	12.857%	$192.8613	$192.86	$192.85	$192.90
Purchase #5	$96.42	4.488%	$100.7473	$100.75	$100.75	$100.70
Purchase #6	$150.88	7.474%	$162.1568	$162.16	$162.15	$162.20
Purchase #7	$210.39	10.498%	$232.4767	$232.48	$232.50	$232.50
7 purchase totals =	$1,247.77		$1,341.2755	$1,341.28	$1,341.30	$1,341.30