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	$30.31	5.440%	$31.9589	$31.96	$31.95	$32.00
Purchase #2	$241.48	12.735%	$272.2325	$272.23	$272.25	$272.20
Purchase #3	$139.54	5.354%	$147.011	$147.01	$147.00	$147.00
Purchase #4	$92.83	8.607%	$100.8199	$100.82	$100.80	$100.80
Purchase #5	$66.88	7.727%	$72.0478	$72.05	$72.05	$72.00
Purchase #6	$119.76	10.220%	$131.9995	$132.00	$132.00	$132.00
Purchase #7	$76.98	11.487%	$85.8227	$85.82	$85.80	$85.80
7 purchase totals =	$767.78		$841.8923	$841.89	$841.85	$841.80