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	$159.59	6.472%	$169.9187	$169.92	$169.90	$169.90
Purchase #2	$61.45	4.447%	$64.1827	$64.18	$64.20	$64.20
Purchase #3	$87.50	8.238%	$94.7083	$94.71	$94.70	$94.70
Purchase #4	$31.89	6.464%	$33.9514	$33.95	$33.95	$34.00
Purchase #5	$133.80	10.533%	$147.8932	$147.89	$147.90	$147.90
Purchase #6	$148.48	5.675%	$156.9062	$156.91	$156.90	$156.90
Purchase #7	$179.62	11.528%	$200.3266	$200.33	$200.35	$200.30
7 purchase totals =	$802.33		$867.8871	$867.89	$867.90	$867.90