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	$175.93	12.700%	$198.2731	$198.27	$198.25	$198.30
Purchase #2	$20.85	12.462%	$23.4483	$23.45	$23.45	$23.40
Purchase #3	$39.31	9.798%	$43.1616	$43.16	$43.15	$43.20
Purchase #4	$31.90	12.485%	$35.8827	$35.88	$35.90	$35.90
Purchase #5	$125.90	13.591%	$143.0111	$143.01	$143.00	$143.00
Purchase #6	$133.25	13.407%	$151.1148	$151.11	$151.10	$151.10
Purchase #7	$64.64	11.756%	$72.2391	$72.24	$72.25	$72.20
7 purchase totals =	$591.78		$667.1307	$667.12	$667.10	$667.10