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	$95.82	10.849%	$106.2155	$106.22	$106.20	$106.20
Purchase #2	$85.31	11.115%	$94.7922	$94.79	$94.80	$94.80
Purchase #3	$170.56	11.224%	$189.7037	$189.70	$189.70	$189.70
Purchase #4	$98.32	5.266%	$103.4975	$103.50	$103.50	$103.50
Purchase #5	$153.75	12.281%	$172.632	$172.63	$172.65	$172.60
Purchase #6	$224.94	10.319%	$248.1516	$248.15	$248.15	$248.20
Purchase #7	$14.30	8.171%	$15.4685	$15.47	$15.45	$15.50
7 purchase totals =	$843.00		$930.4610	$930.46	$930.45	$930.50