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	$137.31	3.764%	$142.4783	$142.48	$142.50	$142.50
Purchase #2	$25.76	6.290%	$27.3803	$27.38	$27.40	$27.40
Purchase #3	$178.39	13.678%	$202.7902	$202.79	$202.80	$202.80
Purchase #4	$240.69	12.707%	$271.2745	$271.27	$271.25	$271.30
Purchase #5	$97.77	5.227%	$102.8804	$102.88	$102.90	$102.90
Purchase #6	$184.50	6.562%	$196.6069	$196.61	$196.60	$196.60
Purchase #7	$133.58	13.636%	$151.795	$151.80	$151.80	$151.80
7 purchase totals =	$998.00		$1,095.2056	$1,095.21	$1,095.25	$1,095.30