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	$47.31	7.538%	$50.8762	$50.88	$50.90	$50.90
Purchase #2	$212.25	11.809%	$237.3146	$237.31	$237.30	$237.30
Purchase #3	$74.51	7.520%	$80.1132	$80.11	$80.10	$80.10
Purchase #4	$49.51	6.264%	$52.6113	$52.61	$52.60	$52.60
Purchase #5	$119.86	11.770%	$133.9675	$133.97	$133.95	$134.00
Purchase #6	$76.58	7.849%	$82.5908	$82.59	$82.60	$82.60
Purchase #7	$47.38	4.498%	$49.5112	$49.51	$49.50	$49.50
7 purchase totals =	$627.40		$686.9848	$686.98	$686.95	$687.00