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	$142.57	9.627%	$156.2952	$156.30	$156.30	$156.30
Purchase #2	$196.38	6.565%	$209.2723	$209.27	$209.25	$209.30
Purchase #3	$127.43	3.158%	$131.4542	$131.45	$131.45	$131.50
Purchase #4	$161.43	5.188%	$169.805	$169.81	$169.80	$169.80
Purchase #5	$220.55	10.142%	$242.9182	$242.92	$242.90	$242.90
Purchase #6	$100.64	11.499%	$112.2126	$112.21	$112.20	$112.20
Purchase #7	$197.55	11.567%	$220.4006	$220.40	$220.40	$220.40
7 purchase totals =	$1,146.55		$1,242.3581	$1,242.36	$1,242.30	$1,242.40