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	$74.65	12.720%	$84.1455	$84.15	$84.15	$84.10
Purchase #2	$86.28	6.177%	$91.6095	$91.61	$91.60	$91.60
Purchase #3	$52.62	13.620%	$59.7868	$59.79	$59.80	$59.80
Purchase #4	$249.91	5.675%	$264.0924	$264.09	$264.10	$264.10
Purchase #5	$147.28	10.419%	$162.6251	$162.63	$162.65	$162.60
Purchase #6	$62.25	4.654%	$65.1471	$65.15	$65.15	$65.10
Purchase #7	$155.67	3.334%	$160.86	$160.86	$160.85	$160.90
7 purchase totals =	$828.66		$888.2664	$888.28	$888.30	$888.20