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	$87.83	6.691%	$93.7067	$93.71	$93.70	$93.70
Purchase #2	$83.63	7.805%	$90.1573	$90.16	$90.15	$90.20
Purchase #3	$115.94	9.863%	$127.3752	$127.38	$127.40	$127.40
Purchase #4	$73.82	8.619%	$80.1825	$80.18	$80.20	$80.20
Purchase #5	$43.39	4.140%	$45.1863	$45.19	$45.20	$45.20
Purchase #6	$136.29	13.286%	$154.3975	$154.40	$154.40	$154.40
Purchase #7	$171.59	4.573%	$179.4368	$179.44	$179.45	$179.40
7 purchase totals =	$712.49		$770.4423	$770.46	$770.50	$770.50