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	$14.98	6.125%	$15.8975	$15.90	$15.90	$15.90
Purchase #2	$141.76	4.512%	$148.1562	$148.16	$148.15	$148.20
Purchase #3	$11.38	11.731%	$12.715	$12.72	$12.70	$12.70
Purchase #4	$171.50	9.701%	$188.1372	$188.14	$188.15	$188.10
Purchase #5	$78.65	6.249%	$83.5648	$83.56	$83.55	$83.60
Purchase #6	$150.86	7.839%	$162.6859	$162.69	$162.70	$162.70
Purchase #7	$148.44	4.234%	$154.7249	$154.72	$154.70	$154.70
7 purchase totals =	$717.57		$765.8815	$765.89	$765.85	$765.90