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	$126.74	10.857%	$140.5002	$140.50	$140.50	$140.50
Purchase #2	$62.96	11.573%	$70.2464	$70.25	$70.25	$70.20
Purchase #3	$246.72	3.421%	$255.1603	$255.16	$255.15	$255.20
Purchase #4	$96.59	13.770%	$109.8904	$109.89	$109.90	$109.90
Purchase #5	$116.91	13.805%	$133.0494	$133.05	$133.05	$133.00
Purchase #6	$148.85	13.395%	$168.7885	$168.79	$168.80	$168.80
Purchase #7	$27.26	5.433%	$28.741	$28.74	$28.75	$28.70
7 purchase totals =	$826.03		$906.3762	$906.38	$906.40	$906.30