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	$137.89	13.745%	$156.843	$156.84	$156.85	$156.80
Purchase #2	$50.43	3.857%	$52.3751	$52.38	$52.40	$52.40
Purchase #3	$161.83	7.259%	$173.5772	$173.58	$173.60	$173.60
Purchase #4	$180.33	8.870%	$196.3253	$196.33	$196.35	$196.30
Purchase #5	$198.36	11.366%	$220.9056	$220.91	$220.90	$220.90
Purchase #6	$102.96	6.776%	$109.9366	$109.94	$109.95	$109.90
Purchase #7	$26.91	6.315%	$28.6094	$28.61	$28.60	$28.60
7 purchase totals =	$858.71		$938.5722	$938.59	$938.65	$938.50