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	$145.51	12.786%	$164.1149	$164.11	$164.10	$164.10
Purchase #2	$113.63	8.436%	$123.2158	$123.22	$123.20	$123.20
Purchase #3	$48.67	3.867%	$50.5521	$50.55	$50.55	$50.60
Purchase #4	$83.37	7.580%	$89.6894	$89.69	$89.70	$89.70
Purchase #5	$88.88	11.304%	$98.927	$98.93	$98.95	$98.90
Purchase #6	$219.96	13.270%	$249.1487	$249.15	$249.15	$249.10
Purchase #7	$186.96	10.613%	$206.8021	$206.80	$206.80	$206.80
7 purchase totals =	$886.98		$982.4500	$982.45	$982.45	$982.40