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	$90.53	10.568%	$100.0972	$100.10	$100.10	$100.10
Purchase #2	$141.94	10.853%	$157.3447	$157.34	$157.35	$157.30
Purchase #3	$200.63	10.592%	$221.8807	$221.88	$221.90	$221.90
Purchase #4	$198.99	5.272%	$209.4808	$209.48	$209.50	$209.50
Purchase #5	$40.71	7.166%	$43.6273	$43.63	$43.65	$43.60
Purchase #6	$174.71	5.696%	$184.6615	$184.66	$184.65	$184.70
Purchase #7	$128.72	12.120%	$144.3209	$144.32	$144.30	$144.30
7 purchase totals =	$976.23		$1,061.4131	$1,061.41	$1,061.45	$1,061.40