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	$81.64	8.635%	$88.6896	$88.69	$88.70	$88.70
Purchase #2	$36.40	12.464%	$40.9369	$40.94	$40.95	$40.90
Purchase #3	$190.42	12.581%	$214.3767	$214.38	$214.40	$214.40
Purchase #4	$51.63	6.331%	$54.8987	$54.90	$54.90	$54.90
Purchase #5	$121.79	7.566%	$131.0046	$131.00	$131.00	$131.00
Purchase #6	$35.86	4.562%	$37.4959	$37.50	$37.50	$37.50
Purchase #7	$183.50	8.737%	$199.5324	$199.53	$199.55	$199.50
7 purchase totals =	$701.24		$766.9348	$766.94	$767.00	$766.90