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	$150.44	12.281%	$168.9155	$168.92	$168.90	$168.90
Purchase #2	$52.83	12.272%	$59.3133	$59.31	$59.30	$59.30
Purchase #3	$154.26	10.117%	$169.8665	$169.87	$169.85	$169.90
Purchase #4	$42.57	5.465%	$44.8965	$44.90	$44.90	$44.90
Purchase #5	$86.43	10.441%	$95.4542	$95.45	$95.45	$95.50
Purchase #6	$232.66	13.643%	$264.4018	$264.40	$264.40	$264.40
Purchase #7	$94.93	4.651%	$99.3452	$99.35	$99.35	$99.30
7 purchase totals =	$814.12		$902.1930	$902.20	$902.15	$902.20