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	$14.38	10.732%	$15.9233	$15.92	$15.90	$15.90
Purchase #2	$112.68	9.291%	$123.1491	$123.15	$123.15	$123.10
Purchase #3	$149.30	10.120%	$164.4092	$164.41	$164.40	$164.40
Purchase #4	$16.94	9.160%	$18.4917	$18.49	$18.50	$18.50
Purchase #5	$45.76	3.764%	$47.4824	$47.48	$47.50	$47.50
Purchase #6	$192.34	8.759%	$209.1871	$209.19	$209.20	$209.20
Purchase #7	$82.48	11.220%	$91.7343	$91.73	$91.75	$91.70
7 purchase totals =	$613.88		$670.3771	$670.37	$670.40	$670.30