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	$80.84	12.227%	$90.7243	$90.72	$90.70	$90.70
Purchase #2	$98.25	11.779%	$109.8229	$109.82	$109.80	$109.80
Purchase #3	$133.61	10.424%	$147.5375	$147.54	$147.55	$147.50
Purchase #4	$107.75	5.203%	$113.3562	$113.36	$113.35	$113.40
Purchase #5	$104.71	4.620%	$109.5476	$109.55	$109.55	$109.50
Purchase #6	$35.79	9.755%	$39.2813	$39.28	$39.30	$39.30
Purchase #7	$9.49	5.142%	$9.978	$9.98	$10.00	$10.00
7 purchase totals =	$570.44		$620.2478	$620.25	$620.25	$620.20