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	$141.68	6.205%	$150.4712	$150.47	$150.45	$150.50
Purchase #2	$226.96	10.104%	$249.892	$249.89	$249.90	$249.90
Purchase #3	$235.29	9.721%	$258.1625	$258.16	$258.15	$258.20
Purchase #4	$18.93	6.502%	$20.1608	$20.16	$20.15	$20.20
Purchase #5	$242.46	7.327%	$260.225	$260.23	$260.25	$260.20
Purchase #6	$41.73	4.804%	$43.7347	$43.73	$43.75	$43.70
Purchase #7	$96.29	9.491%	$105.4289	$105.43	$105.45	$105.40
7 purchase totals =	$1,003.34		$1,088.0751	$1,088.07	$1,088.10	$1,088.10