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	$30.39	12.544%	$34.2021	$34.20	$34.20	$34.20
Purchase #2	$242.47	10.594%	$268.1573	$268.16	$268.15	$268.20
Purchase #3	$98.71	12.709%	$111.2551	$111.26	$111.25	$111.30
Purchase #4	$154.49	10.804%	$171.1811	$171.18	$171.20	$171.20
Purchase #5	$225.54	4.128%	$234.8503	$234.85	$234.85	$234.90
Purchase #6	$99.76	11.523%	$111.2553	$111.26	$111.25	$111.30
Purchase #7	$64.87	9.527%	$71.0502	$71.05	$71.05	$71.10
7 purchase totals =	$916.23		$1,001.9514	$1,001.96	$1,001.95	$1,002.20