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	$209.98	13.359%	$238.0312	$238.03	$238.05	$238.00
Purchase #2	$53.81	9.358%	$58.8455	$58.85	$58.85	$58.80
Purchase #3	$215.89	8.179%	$233.5476	$233.55	$233.55	$233.50
Purchase #4	$82.64	9.867%	$90.7941	$90.79	$90.80	$90.80
Purchase #5	$85.54	4.361%	$89.2704	$89.27	$89.25	$89.30
Purchase #6	$170.91	5.664%	$180.5903	$180.59	$180.60	$180.60
Purchase #7	$204.86	12.259%	$229.9738	$229.97	$229.95	$230.00
7 purchase totals =	$1,023.63		$1,121.0529	$1,121.05	$1,121.05	$1,121.00