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	$120.59	8.592%	$130.9511	$130.95	$130.95	$131.00
Purchase #2	$92.78	12.747%	$104.6067	$104.61	$104.60	$104.60
Purchase #3	$137.28	3.130%	$141.5769	$141.58	$141.60	$141.60
Purchase #4	$120.45	4.300%	$125.6294	$125.63	$125.65	$125.60
Purchase #5	$204.52	8.724%	$222.3623	$222.36	$222.35	$222.40
Purchase #6	$228.83	3.494%	$236.8253	$236.83	$236.85	$236.80
Purchase #7	$17.93	3.317%	$18.5247	$18.52	$18.50	$18.50
7 purchase totals =	$922.38		$980.4764	$980.48	$980.50	$980.50