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	$76.82	8.368%	$83.2483	$83.25	$83.25	$83.20
Purchase #2	$41.33	12.132%	$46.3442	$46.34	$46.35	$46.30
Purchase #3	$178.72	3.306%	$184.6285	$184.63	$184.65	$184.60
Purchase #4	$78.41	4.623%	$82.0349	$82.03	$82.05	$82.00
Purchase #5	$219.82	12.826%	$248.0141	$248.01	$248.00	$248.00
Purchase #6	$63.34	6.597%	$67.5185	$67.52	$67.50	$67.50
Purchase #7	$229.30	8.501%	$248.7928	$248.79	$248.80	$248.80
7 purchase totals =	$887.74		$960.5813	$960.57	$960.60	$960.40