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	$87.83	4.132%	$91.4591	$91.46	$91.45	$91.50
Purchase #2	$65.63	8.424%	$71.1587	$71.16	$71.15	$71.20
Purchase #3	$123.38	6.751%	$131.7094	$131.71	$131.70	$131.70
Purchase #4	$133.81	10.778%	$148.232	$148.23	$148.25	$148.20
Purchase #5	$51.39	13.417%	$58.285	$58.29	$58.30	$58.30
Purchase #6	$36.41	10.512%	$40.2374	$40.24	$40.25	$40.20
Purchase #7	$119.85	3.805%	$124.4103	$124.41	$124.40	$124.40
7 purchase totals =	$618.30		$665.4919	$665.50	$665.50	$665.50