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	$131.61	4.415%	$137.4206	$137.42	$137.40	$137.40
Purchase #2	$37.80	12.572%	$42.5522	$42.55	$42.55	$42.60
Purchase #3	$160.30	11.798%	$179.2122	$179.21	$179.20	$179.20
Purchase #4	$246.44	13.328%	$279.2855	$279.29	$279.30	$279.30
Purchase #5	$84.41	13.624%	$95.91	$95.91	$95.90	$95.90
Purchase #6	$110.32	13.820%	$125.5662	$125.57	$125.55	$125.60
Purchase #7	$116.53	6.252%	$123.8155	$123.82	$123.80	$123.80
7 purchase totals =	$887.41		$983.7622	$983.77	$983.70	$983.80