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	$123.88	3.428%	$128.1266	$128.13	$128.15	$128.10
Purchase #2	$131.71	3.485%	$136.3001	$136.30	$136.30	$136.30
Purchase #3	$89.94	6.682%	$95.9498	$95.95	$95.95	$95.90
Purchase #4	$77.37	7.138%	$82.8927	$82.89	$82.90	$82.90
Purchase #5	$87.58	11.250%	$97.4328	$97.43	$97.45	$97.40
Purchase #6	$185.64	6.815%	$198.2914	$198.29	$198.30	$198.30
Purchase #7	$25.83	5.359%	$27.2142	$27.21	$27.20	$27.20
7 purchase totals =	$721.95		$766.2076	$766.20	$766.25	$766.10