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	$85.29	6.249%	$90.6198	$90.62	$90.60	$90.60
Purchase #2	$170.41	10.681%	$188.6115	$188.61	$188.60	$188.60
Purchase #3	$108.72	10.379%	$120.004	$120.00	$120.00	$120.00
Purchase #4	$191.61	7.566%	$206.1072	$206.11	$206.10	$206.10
Purchase #5	$13.76	12.835%	$15.5261	$15.53	$15.55	$15.50
Purchase #6	$227.91	11.152%	$253.3265	$253.33	$253.35	$253.30
Purchase #7	$71.49	9.502%	$78.283	$78.28	$78.30	$78.30
7 purchase totals =	$869.19		$952.4781	$952.48	$952.50	$952.40