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	$237.83	5.421%	$250.7228	$250.72	$250.70	$250.70
Purchase #2	$200.70	4.863%	$210.46	$210.46	$210.45	$210.50
Purchase #3	$168.53	5.122%	$177.1621	$177.16	$177.15	$177.20
Purchase #4	$175.44	13.596%	$199.2928	$199.29	$199.30	$199.30
Purchase #5	$244.87	7.686%	$263.6907	$263.69	$263.70	$263.70
Purchase #6	$87.69	13.470%	$99.5018	$99.50	$99.50	$99.50
Purchase #7	$102.81	6.527%	$109.5204	$109.52	$109.50	$109.50
7 purchase totals =	$1,217.87		$1,310.3506	$1,310.34	$1,310.30	$1,310.40