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	$118.46	4.586%	$123.8926	$123.89	$123.90	$123.90
Purchase #2	$125.96	7.172%	$134.9939	$134.99	$135.00	$135.00
Purchase #3	$90.61	7.537%	$97.4393	$97.44	$97.45	$97.40
Purchase #4	$12.93	12.759%	$14.5797	$14.58	$14.60	$14.60
Purchase #5	$90.46	9.559%	$99.1071	$99.11	$99.10	$99.10
Purchase #6	$192.87	13.239%	$218.4041	$218.40	$218.40	$218.40
Purchase #7	$40.58	4.522%	$42.415	$42.42	$42.40	$42.40
7 purchase totals =	$671.87		$730.8317	$730.83	$730.85	$730.80