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	$34.98	7.702%	$37.6742	$37.67	$37.65	$37.70
Purchase #2	$99.61	3.481%	$103.0774	$103.08	$103.10	$103.10
Purchase #3	$71.33	8.151%	$77.1441	$77.14	$77.15	$77.10
Purchase #4	$39.86	9.309%	$43.5706	$43.57	$43.55	$43.60
Purchase #5	$143.82	3.282%	$148.5402	$148.54	$148.55	$148.50
Purchase #6	$119.31	3.492%	$123.4763	$123.48	$123.50	$123.50
Purchase #7	$244.92	7.836%	$264.1119	$264.11	$264.10	$264.10
7 purchase totals =	$753.83		$797.5947	$797.59	$797.60	$797.60