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	$42.63	8.218%	$46.1333	$46.13	$46.15	$46.10
Purchase #2	$200.74	5.696%	$212.1742	$212.17	$212.15	$212.20
Purchase #3	$250.92	3.573%	$259.8854	$259.89	$259.90	$259.90
Purchase #4	$232.89	10.106%	$256.4259	$256.43	$256.45	$256.40
Purchase #5	$201.49	3.687%	$208.9189	$208.92	$208.90	$208.90
Purchase #6	$181.92	3.797%	$188.8275	$188.83	$188.85	$188.80
Purchase #7	$79.70	7.815%	$85.9286	$85.93	$85.95	$85.90
7 purchase totals =	$1,190.29		$1,258.2938	$1,258.30	$1,258.35	$1,258.20