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	$76.36	13.229%	$86.4617	$86.46	$86.45	$86.50
Purchase #2	$120.84	12.741%	$136.2362	$136.24	$136.25	$136.20
Purchase #3	$199.50	11.525%	$222.4924	$222.49	$222.50	$222.50
Purchase #4	$94.67	7.187%	$101.4739	$101.47	$101.45	$101.50
Purchase #5	$35.53	7.666%	$38.2537	$38.25	$38.25	$38.30
Purchase #6	$108.97	13.821%	$124.0307	$124.03	$124.05	$124.00
Purchase #7	$95.39	5.630%	$100.7605	$100.76	$100.75	$100.80
7 purchase totals =	$731.26		$809.7091	$809.70	$809.70	$809.80