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	$99.75	4.737%	$104.4752	$104.48	$104.50	$104.50
Purchase #2	$153.99	11.713%	$172.0268	$172.03	$172.05	$172.00
Purchase #3	$6.95	12.337%	$7.8074	$7.81	$7.80	$7.80
Purchase #4	$80.46	12.223%	$90.2946	$90.29	$90.30	$90.30
Purchase #5	$79.85	4.596%	$83.5199	$83.52	$83.50	$83.50
Purchase #6	$143.87	11.375%	$160.2352	$160.24	$160.25	$160.20
Purchase #7	$110.82	9.717%	$121.5884	$121.59	$121.60	$121.60
7 purchase totals =	$675.69		$739.9475	$739.96	$740.00	$739.90