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	$100.61	9.117%	$109.7826	$109.78	$109.80	$109.80
Purchase #2	$233.59	10.541%	$258.2127	$258.21	$258.20	$258.20
Purchase #3	$38.48	5.296%	$40.5179	$40.52	$40.50	$40.50
Purchase #4	$178.84	7.678%	$192.5713	$192.57	$192.55	$192.60
Purchase #5	$87.26	9.129%	$95.226	$95.23	$95.25	$95.20
Purchase #6	$59.63	12.520%	$67.0957	$67.10	$67.10	$67.10
Purchase #7	$81.80	5.326%	$86.1567	$86.16	$86.15	$86.20
7 purchase totals =	$780.21		$849.5629	$849.57	$849.55	$849.60