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	$214.85	13.348%	$243.5282	$243.53	$243.55	$243.50
Purchase #2	$230.71	4.817%	$241.8233	$241.82	$241.80	$241.80
Purchase #3	$73.26	3.654%	$75.9369	$75.94	$75.95	$75.90
Purchase #4	$182.35	4.136%	$189.892	$189.89	$189.90	$189.90
Purchase #5	$147.40	5.537%	$155.5615	$155.56	$155.55	$155.60
Purchase #6	$150.58	7.789%	$162.3087	$162.31	$162.30	$162.30
Purchase #7	$223.88	3.323%	$231.3195	$231.32	$231.30	$231.30
7 purchase totals =	$1,223.03		$1,300.3701	$1,300.37	$1,300.35	$1,300.30