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	$113.98	10.697%	$126.1724	$126.17	$126.15	$126.20
Purchase #2	$95.52	9.104%	$104.2161	$104.22	$104.20	$104.20
Purchase #3	$197.39	6.296%	$209.8177	$209.82	$209.80	$209.80
Purchase #4	$248.75	10.419%	$274.6673	$274.67	$274.65	$274.70
Purchase #5	$178.89	12.275%	$200.8487	$200.85	$200.85	$200.80
Purchase #6	$68.73	11.317%	$76.5082	$76.51	$76.50	$76.50
Purchase #7	$6.51	10.114%	$7.1684	$7.17	$7.15	$7.20
7 purchase totals =	$909.77		$999.3988	$999.41	$999.30	$999.40