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	$37.54	9.484%	$41.1003	$41.10	$41.10	$41.10
Purchase #2	$91.30	8.641%	$99.1892	$99.19	$99.20	$99.20
Purchase #3	$93.62	5.232%	$98.5182	$98.52	$98.50	$98.50
Purchase #4	$76.60	8.250%	$82.9195	$82.92	$82.90	$82.90
Purchase #5	$11.90	11.349%	$13.2505	$13.25	$13.25	$13.30
Purchase #6	$206.33	3.691%	$213.9456	$213.95	$213.95	$213.90
Purchase #7	$145.80	4.180%	$151.8944	$151.89	$151.90	$151.90
7 purchase totals =	$663.09		$700.8177	$700.82	$700.80	$700.80