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	$182.67	3.727%	$189.4781	$189.48	$189.50	$189.50
Purchase #2	$143.26	6.708%	$152.8699	$152.87	$152.85	$152.90
Purchase #3	$215.28	10.361%	$237.5852	$237.59	$237.60	$237.60
Purchase #4	$222.83	5.117%	$234.2322	$234.23	$234.25	$234.20
Purchase #5	$72.70	7.402%	$78.0813	$78.08	$78.10	$78.10
Purchase #6	$209.34	4.267%	$218.2725	$218.27	$218.25	$218.30
Purchase #7	$143.43	3.712%	$148.7541	$148.75	$148.75	$148.80
7 purchase totals =	$1,189.51		$1,259.2733	$1,259.27	$1,259.30	$1,259.40