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	$31.49	7.518%	$33.8574	$33.86	$33.85	$33.90
Purchase #2	$199.71	5.583%	$210.8598	$210.86	$210.85	$210.90
Purchase #3	$185.89	5.357%	$195.8481	$195.85	$195.85	$195.80
Purchase #4	$157.70	3.871%	$163.8046	$163.80	$163.80	$163.80
Purchase #5	$83.33	8.200%	$90.1631	$90.16	$90.15	$90.20
Purchase #6	$116.29	6.257%	$123.5663	$123.57	$123.55	$123.60
Purchase #7	$146.82	4.751%	$153.7954	$153.80	$153.80	$153.80
7 purchase totals =	$921.23		$971.8947	$971.90	$971.85	$972.00