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	$39.31	9.335%	$42.9796	$42.98	$43.00	$43.00
Purchase #2	$36.90	10.628%	$40.8217	$40.82	$40.80	$40.80
Purchase #3	$156.48	9.309%	$171.0467	$171.05	$171.05	$171.00
Purchase #4	$64.51	9.564%	$70.6797	$70.68	$70.70	$70.70
Purchase #5	$40.59	6.847%	$43.3692	$43.37	$43.35	$43.40
Purchase #6	$36.65	3.168%	$37.8111	$37.81	$37.80	$37.80
Purchase #7	$80.91	3.373%	$83.6391	$83.64	$83.65	$83.60
7 purchase totals =	$455.35		$490.3471	$490.35	$490.35	$490.30