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	$175.34	13.106%	$198.3201	$198.32	$198.30	$198.30
Purchase #2	$133.88	5.575%	$141.3438	$141.34	$141.35	$141.30
Purchase #3	$46.37	4.298%	$48.363	$48.36	$48.35	$48.40
Purchase #4	$6.77	10.704%	$7.4947	$7.49	$7.50	$7.50
Purchase #5	$41.95	3.159%	$43.2752	$43.28	$43.30	$43.30
Purchase #6	$162.92	7.697%	$175.46	$175.46	$175.45	$175.50
Purchase #7	$151.94	12.834%	$171.44	$171.44	$171.45	$171.40
7 purchase totals =	$719.17		$785.6968	$785.69	$785.70	$785.70