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	$118.96	3.535%	$123.1652	$123.17	$123.15	$123.20
Purchase #2	$83.95	11.497%	$93.6017	$93.60	$93.60	$93.60
Purchase #3	$144.77	12.316%	$162.5999	$162.60	$162.60	$162.60
Purchase #4	$6.78	5.770%	$7.1712	$7.17	$7.15	$7.20
Purchase #5	$89.93	12.727%	$101.3754	$101.38	$101.40	$101.40
Purchase #6	$92.37	10.604%	$102.1649	$102.16	$102.15	$102.20
Purchase #7	$35.97	12.262%	$40.3806	$40.38	$40.40	$40.40
7 purchase totals =	$572.73		$630.4589	$630.46	$630.45	$630.60