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	$18.55	3.417%	$19.1839	$19.18	$19.20	$19.20
Purchase #2	$100.66	8.647%	$109.3641	$109.36	$109.35	$109.40
Purchase #3	$173.97	6.340%	$184.9997	$185.00	$185.00	$185.00
Purchase #4	$224.89	7.540%	$241.8467	$241.85	$241.85	$241.80
Purchase #5	$51.89	7.570%	$55.8181	$55.82	$55.80	$55.80
Purchase #6	$7.48	3.430%	$7.7366	$7.74	$7.75	$7.70
Purchase #7	$104.33	5.373%	$109.9357	$109.94	$109.95	$109.90
7 purchase totals =	$681.77		$728.8848	$728.89	$728.90	$728.80