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	$128.41	3.697%	$133.1573	$133.16	$133.15	$133.20
Purchase #2	$182.66	4.510%	$190.898	$190.90	$190.90	$190.90
Purchase #3	$32.36	9.350%	$35.3857	$35.39	$35.40	$35.40
Purchase #4	$160.80	5.591%	$169.7903	$169.79	$169.80	$169.80
Purchase #5	$109.43	3.358%	$113.1047	$113.10	$113.10	$113.10
Purchase #6	$75.91	9.124%	$82.836	$82.84	$82.85	$82.80
Purchase #7	$112.80	9.853%	$123.9142	$123.91	$123.90	$123.90
7 purchase totals =	$802.37		$849.0862	$849.09	$849.10	$849.10