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	$18.74	11.315%	$20.8604	$20.86	$20.85	$20.90
Purchase #2	$11.89	4.764%	$12.4564	$12.46	$12.45	$12.50
Purchase #3	$232.89	12.772%	$262.6347	$262.63	$262.65	$262.60
Purchase #4	$97.66	4.442%	$101.9981	$102.00	$102.00	$102.00
Purchase #5	$118.62	8.404%	$128.5888	$128.59	$128.60	$128.60
Purchase #6	$207.51	4.319%	$216.4724	$216.47	$216.45	$216.50
Purchase #7	$240.54	13.822%	$273.7874	$273.79	$273.80	$273.80
7 purchase totals =	$927.85		$1,016.7982	$1,016.80	$1,016.80	$1,016.90