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	$135.99	11.212%	$151.2372	$151.24	$151.25	$151.20
Purchase #2	$223.54	8.469%	$242.4716	$242.47	$242.45	$242.50
Purchase #3	$145.51	6.578%	$155.0816	$155.08	$155.10	$155.10
Purchase #4	$106.30	12.786%	$119.8915	$119.89	$119.90	$119.90
Purchase #5	$117.93	11.696%	$131.7231	$131.72	$131.70	$131.70
Purchase #6	$185.25	11.692%	$206.9094	$206.91	$206.90	$206.90
Purchase #7	$108.76	13.741%	$123.7047	$123.70	$123.70	$123.70
7 purchase totals =	$1,023.28		$1,131.0191	$1,131.01	$1,131.00	$1,131.00