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	$202.72	9.662%	$222.3068	$222.31	$222.30	$222.30
Purchase #2	$69.97	5.133%	$73.5616	$73.56	$73.55	$73.60
Purchase #3	$42.71	12.661%	$48.1175	$48.12	$48.10	$48.10
Purchase #4	$192.50	8.840%	$209.517	$209.52	$209.50	$209.50
Purchase #5	$99.96	4.233%	$104.1913	$104.19	$104.20	$104.20
Purchase #6	$123.32	10.693%	$136.5066	$136.51	$136.50	$136.50
Purchase #7	$35.47	4.786%	$37.1676	$37.17	$37.15	$37.20
7 purchase totals =	$766.65		$831.3684	$831.38	$831.30	$831.40