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	$172.53	10.295%	$190.292	$190.29	$190.30	$190.30
Purchase #2	$170.41	7.636%	$183.4225	$183.42	$183.40	$183.40
Purchase #3	$170.76	5.734%	$180.5514	$180.55	$180.55	$180.60
Purchase #4	$98.88	10.706%	$109.4661	$109.47	$109.45	$109.50
Purchase #5	$71.74	12.254%	$80.531	$80.53	$80.55	$80.50
Purchase #6	$66.62	6.631%	$71.0376	$71.04	$71.05	$71.00
Purchase #7	$143.79	5.394%	$151.546	$151.55	$151.55	$151.50
7 purchase totals =	$894.73		$966.8466	$966.85	$966.85	$966.80