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	$153.45	8.425%	$166.3782	$166.38	$166.40	$166.40
Purchase #2	$209.47	9.212%	$228.7664	$228.77	$228.75	$228.80
Purchase #3	$67.29	8.696%	$73.1415	$73.14	$73.15	$73.10
Purchase #4	$99.90	5.761%	$105.6552	$105.66	$105.65	$105.70
Purchase #5	$113.56	5.457%	$119.757	$119.76	$119.75	$119.80
Purchase #6	$14.67	7.865%	$15.8238	$15.82	$15.80	$15.80
Purchase #7	$198.46	12.527%	$223.3211	$223.32	$223.30	$223.30
7 purchase totals =	$856.80		$932.8432	$932.85	$932.80	$932.90