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	$96.82	9.368%	$105.8901	$105.89	$105.90	$105.90
Purchase #2	$6.59	13.715%	$7.4938	$7.49	$7.50	$7.50
Purchase #3	$195.81	11.124%	$217.5919	$217.59	$217.60	$217.60
Purchase #4	$226.66	5.279%	$238.6254	$238.63	$238.65	$238.60
Purchase #5	$201.90	3.824%	$209.6207	$209.62	$209.60	$209.60
Purchase #6	$11.25	11.653%	$12.561	$12.56	$12.55	$12.60
Purchase #7	$41.85	12.329%	$47.0097	$47.01	$47.00	$47.00
7 purchase totals =	$780.88		$838.7926	$838.79	$838.80	$838.80