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	$210.29	4.731%	$220.2388	$220.24	$220.25	$220.20
Purchase #2	$245.75	11.422%	$273.8196	$273.82	$273.80	$273.80
Purchase #3	$116.93	8.707%	$127.1111	$127.11	$127.10	$127.10
Purchase #4	$148.59	9.654%	$162.9349	$162.93	$162.95	$162.90
Purchase #5	$192.76	4.191%	$200.8386	$200.84	$200.85	$200.80
Purchase #6	$150.84	8.768%	$164.0657	$164.07	$164.05	$164.10
Purchase #7	$116.51	10.584%	$128.8414	$128.84	$128.85	$128.80
7 purchase totals =	$1,181.67		$1,277.8501	$1,277.85	$1,277.85	$1,277.70