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	$82.52	6.535%	$87.9127	$87.91	$87.90	$87.90
Purchase #2	$208.52	5.282%	$219.534	$219.53	$219.55	$219.50
Purchase #3	$174.39	12.398%	$196.0109	$196.01	$196.00	$196.00
Purchase #4	$70.79	13.664%	$80.4627	$80.46	$80.45	$80.50
Purchase #5	$77.33	6.333%	$82.2273	$82.23	$82.25	$82.20
Purchase #6	$237.38	10.847%	$263.1286	$263.13	$263.15	$263.10
Purchase #7	$56.94	6.690%	$60.7493	$60.75	$60.75	$60.70
7 purchase totals =	$907.87		$990.0255	$990.02	$990.05	$989.90