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	$31.75	11.265%	$35.3266	$35.33	$35.35	$35.30
Purchase #2	$163.92	12.190%	$183.9018	$183.90	$183.90	$183.90
Purchase #3	$35.99	13.578%	$40.8767	$40.88	$40.90	$40.90
Purchase #4	$149.29	4.709%	$156.3201	$156.32	$156.30	$156.30
Purchase #5	$139.33	11.441%	$155.2707	$155.27	$155.25	$155.30
Purchase #6	$249.98	13.407%	$283.4948	$283.49	$283.50	$283.50
Purchase #7	$176.85	4.405%	$184.6402	$184.64	$184.65	$184.60
7 purchase totals =	$947.11		$1,039.8309	$1,039.83	$1,039.85	$1,039.80