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	$230.89	5.474%	$243.5289	$243.53	$243.55	$243.50
Purchase #2	$250.48	12.620%	$282.0906	$282.09	$282.10	$282.10
Purchase #3	$186.70	10.788%	$206.8412	$206.84	$206.85	$206.80
Purchase #4	$82.78	9.248%	$90.4355	$90.44	$90.45	$90.40
Purchase #5	$117.73	8.339%	$127.5475	$127.55	$127.55	$127.50
Purchase #6	$69.97	9.193%	$76.4023	$76.40	$76.40	$76.40
Purchase #7	$98.57	11.535%	$109.94	$109.94	$109.95	$109.90
7 purchase totals =	$1,037.12		$1,136.7860	$1,136.79	$1,136.85	$1,136.60