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	$85.86	4.591%	$89.8018	$89.80	$89.80	$89.80
Purchase #2	$136.78	12.106%	$153.3386	$153.34	$153.35	$153.30
Purchase #3	$6.48	4.734%	$6.7868	$6.79	$6.80	$6.80
Purchase #4	$67.78	7.540%	$72.8906	$72.89	$72.90	$72.90
Purchase #5	$115.73	7.630%	$124.5602	$124.56	$124.55	$124.60
Purchase #6	$50.85	5.432%	$53.6122	$53.61	$53.60	$53.60
Purchase #7	$22.48	13.474%	$25.509	$25.51	$25.50	$25.50
7 purchase totals =	$485.96		$526.4992	$526.50	$526.50	$526.50