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	$108.58	10.805%	$120.3121	$120.31	$120.30	$120.30
Purchase #2	$174.94	8.295%	$189.4513	$189.45	$189.45	$189.50
Purchase #3	$40.96	12.198%	$45.9563	$45.96	$45.95	$46.00
Purchase #4	$121.50	3.591%	$125.8631	$125.86	$125.85	$125.90
Purchase #5	$31.79	5.434%	$33.5175	$33.52	$33.50	$33.50
Purchase #6	$56.63	9.275%	$61.8824	$61.88	$61.90	$61.90
Purchase #7	$104.34	8.136%	$112.8291	$112.83	$112.85	$112.80
7 purchase totals =	$638.74		$689.8118	$689.81	$689.80	$689.90