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	$71.78	11.526%	$80.0534	$80.05	$80.05	$80.10
Purchase #2	$215.49	13.850%	$245.3354	$245.34	$245.35	$245.30
Purchase #3	$62.69	13.106%	$70.9062	$70.91	$70.90	$70.90
Purchase #4	$153.79	6.410%	$163.6479	$163.65	$163.65	$163.60
Purchase #5	$142.59	5.816%	$150.883	$150.88	$150.90	$150.90
Purchase #6	$33.30	6.483%	$35.4588	$35.46	$35.45	$35.50
Purchase #7	$246.72	3.555%	$255.4909	$255.49	$255.50	$255.50
7 purchase totals =	$926.36		$1,001.7756	$1,001.78	$1,001.80	$1,001.80