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	$159.83	12.238%	$179.39	$179.39	$179.40	$179.40
Purchase #2	$31.44	6.529%	$33.4927	$33.49	$33.50	$33.50
Purchase #3	$44.66	7.333%	$47.9349	$47.93	$47.95	$47.90
Purchase #4	$208.42	11.298%	$231.9673	$231.97	$231.95	$232.00
Purchase #5	$60.63	9.629%	$66.4681	$66.47	$66.45	$66.50
Purchase #6	$32.39	9.374%	$35.4262	$35.43	$35.45	$35.40
Purchase #7	$79.49	7.172%	$85.191	$85.19	$85.20	$85.20
7 purchase totals =	$616.86		$679.8702	$679.87	$679.90	$679.90