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	$54.59	9.684%	$59.8765	$59.88	$59.90	$59.90
Purchase #2	$75.50	9.830%	$82.9217	$82.92	$82.90	$82.90
Purchase #3	$158.58	8.300%	$171.7421	$171.74	$171.75	$171.70
Purchase #4	$90.90	6.596%	$96.8958	$96.90	$96.90	$96.90
Purchase #5	$28.76	10.638%	$31.8195	$31.82	$31.80	$31.80
Purchase #6	$85.45	8.433%	$92.656	$92.66	$92.65	$92.70
Purchase #7	$183.46	11.712%	$204.9468	$204.95	$204.95	$204.90
7 purchase totals =	$677.24		$740.8584	$740.87	$740.85	$740.80