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	$120.51	11.465%	$134.3265	$134.33	$134.35	$134.30
Purchase #2	$136.96	10.570%	$151.4367	$151.44	$151.45	$151.40
Purchase #3	$179.73	6.428%	$191.283	$191.28	$191.30	$191.30
Purchase #4	$113.93	3.701%	$118.1465	$118.15	$118.15	$118.10
Purchase #5	$189.78	9.837%	$208.4487	$208.45	$208.45	$208.40
Purchase #6	$18.40	11.288%	$20.477	$20.48	$20.50	$20.50
Purchase #7	$60.69	8.723%	$65.984	$65.98	$66.00	$66.00
7 purchase totals =	$820.00		$890.1024	$890.11	$890.20	$890.00