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	$119.57	3.402%	$123.6378	$123.64	$123.65	$123.60
Purchase #2	$161.36	3.734%	$167.3852	$167.39	$167.40	$167.40
Purchase #3	$16.94	9.224%	$18.5025	$18.50	$18.50	$18.50
Purchase #4	$210.85	6.171%	$223.8616	$223.86	$223.85	$223.90
Purchase #5	$169.50	7.725%	$182.5939	$182.59	$182.60	$182.60
Purchase #6	$62.36	3.394%	$64.4765	$64.48	$64.50	$64.50
Purchase #7	$93.92	5.795%	$99.3627	$99.36	$99.35	$99.40
7 purchase totals =	$834.50		$879.8202	$879.82	$879.85	$879.90