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	$136.88	6.134%	$145.2762	$145.28	$145.30	$145.30
Purchase #2	$86.81	7.652%	$93.4527	$93.45	$93.45	$93.50
Purchase #3	$243.48	11.357%	$271.132	$271.13	$271.15	$271.10
Purchase #4	$29.25	10.704%	$32.3809	$32.38	$32.40	$32.40
Purchase #5	$17.93	12.172%	$20.1124	$20.11	$20.10	$20.10
Purchase #6	$202.48	10.112%	$222.9548	$222.95	$222.95	$223.00
Purchase #7	$139.88	4.689%	$146.439	$146.44	$146.45	$146.40
7 purchase totals =	$856.71		$931.7480	$931.74	$931.80	$931.80