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	$84.29	4.153%	$87.7906	$87.79	$87.80	$87.80
Purchase #2	$151.45	11.295%	$168.5563	$168.56	$168.55	$168.60
Purchase #3	$82.75	7.202%	$88.7097	$88.71	$88.70	$88.70
Purchase #4	$249.63	10.411%	$275.619	$275.62	$275.60	$275.60
Purchase #5	$215.30	4.250%	$224.4503	$224.45	$224.45	$224.50
Purchase #6	$56.27	6.142%	$59.7261	$59.73	$59.75	$59.70
Purchase #7	$188.70	10.739%	$208.9645	$208.96	$208.95	$209.00
7 purchase totals =	$1,028.39		$1,113.8165	$1,113.82	$1,113.80	$1,113.90