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	$32.93	11.362%	$36.6715	$36.67	$36.65	$36.70
Purchase #2	$148.37	4.406%	$154.9072	$154.91	$154.90	$154.90
Purchase #3	$82.90	7.117%	$88.8	$88.80	$88.80	$88.80
Purchase #4	$84.89	13.687%	$96.5089	$96.51	$96.50	$96.50
Purchase #5	$62.67	4.472%	$65.4726	$65.47	$65.45	$65.50
Purchase #6	$53.36	7.689%	$57.4629	$57.46	$57.45	$57.50
Purchase #7	$55.28	5.852%	$58.515	$58.52	$58.50	$58.50
7 purchase totals =	$520.40		$558.3381	$558.34	$558.25	$558.40