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	$47.89	12.364%	$53.8111	$53.81	$53.80	$53.80
Purchase #2	$114.92	10.119%	$126.5488	$126.55	$126.55	$126.50
Purchase #3	$37.73	8.420%	$40.9069	$40.91	$40.90	$40.90
Purchase #4	$65.31	7.320%	$70.0907	$70.09	$70.10	$70.10
Purchase #5	$75.90	13.197%	$85.9165	$85.92	$85.90	$85.90
Purchase #6	$91.34	11.386%	$101.74	$101.74	$101.75	$101.70
Purchase #7	$129.88	5.170%	$136.5948	$136.59	$136.60	$136.60
7 purchase totals =	$562.97		$615.6088	$615.61	$615.60	$615.50