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	$72.93	10.155%	$80.336	$80.34	$80.35	$80.30
Purchase #2	$65.63	12.133%	$73.5929	$73.59	$73.60	$73.60
Purchase #3	$35.94	11.671%	$40.1346	$40.13	$40.15	$40.10
Purchase #4	$160.73	9.506%	$176.009	$176.01	$176.00	$176.00
Purchase #5	$234.91	5.556%	$247.9616	$247.96	$247.95	$248.00
Purchase #6	$179.42	9.766%	$196.9422	$196.94	$196.95	$196.90
Purchase #7	$94.35	9.471%	$103.2859	$103.29	$103.30	$103.30
7 purchase totals =	$843.91		$918.2622	$918.26	$918.30	$918.20