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	$85.34	7.315%	$91.5826	$91.58	$91.60	$91.60
Purchase #2	$43.67	8.284%	$47.2876	$47.29	$47.30	$47.30
Purchase #3	$224.43	10.611%	$248.2443	$248.24	$248.25	$248.20
Purchase #4	$57.37	9.573%	$62.862	$62.86	$62.85	$62.90
Purchase #5	$243.53	6.146%	$258.4974	$258.50	$258.50	$258.50
Purchase #6	$119.96	9.503%	$131.3598	$131.36	$131.35	$131.40
Purchase #7	$37.89	3.325%	$39.1498	$39.15	$39.15	$39.10
7 purchase totals =	$812.19		$878.9835	$878.98	$879.00	$879.00