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	$225.66	10.405%	$249.1399	$249.14	$249.15	$249.10
Purchase #2	$40.25	6.150%	$42.7254	$42.73	$42.75	$42.70
Purchase #3	$103.89	10.296%	$114.5865	$114.59	$114.60	$114.60
Purchase #4	$28.98	4.145%	$30.1812	$30.18	$30.20	$30.20
Purchase #5	$87.63	10.620%	$96.9363	$96.94	$96.95	$96.90
Purchase #6	$166.66	12.738%	$187.8892	$187.89	$187.90	$187.90
Purchase #7	$101.98	10.250%	$112.433	$112.43	$112.45	$112.40
7 purchase totals =	$755.05		$833.8915	$833.90	$834.00	$833.80