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	$53.31	9.362%	$58.3009	$58.30	$58.30	$58.30
Purchase #2	$45.67	11.421%	$50.886	$50.89	$50.90	$50.90
Purchase #3	$202.53	7.794%	$218.3152	$218.32	$218.30	$218.30
Purchase #4	$41.45	4.393%	$43.2709	$43.27	$43.25	$43.30
Purchase #5	$142.55	7.681%	$153.4993	$153.50	$153.50	$153.50
Purchase #6	$43.79	10.451%	$48.3665	$48.37	$48.35	$48.40
Purchase #7	$49.96	5.227%	$52.5714	$52.57	$52.55	$52.60
7 purchase totals =	$579.26		$625.2102	$625.22	$625.15	$625.30