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	$85.50	12.349%	$96.0584	$96.06	$96.05	$96.10
Purchase #2	$113.37	10.628%	$125.419	$125.42	$125.40	$125.40
Purchase #3	$123.85	6.170%	$131.4915	$131.49	$131.50	$131.50
Purchase #4	$232.84	5.152%	$244.8359	$244.84	$244.85	$244.80
Purchase #5	$145.58	11.579%	$162.4367	$162.44	$162.45	$162.40
Purchase #6	$37.53	12.249%	$42.127	$42.13	$42.15	$42.10
Purchase #7	$100.63	3.347%	$103.9981	$104.00	$104.00	$104.00
7 purchase totals =	$839.30		$906.3666	$906.38	$906.40	$906.30