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	$49.86	3.316%	$51.5134	$51.51	$51.50	$51.50
Purchase #2	$113.88	4.786%	$119.3303	$119.33	$119.35	$119.30
Purchase #3	$139.65	11.468%	$155.6651	$155.67	$155.65	$155.70
Purchase #4	$94.86	4.409%	$99.0424	$99.04	$99.05	$99.00
Purchase #5	$185.56	5.559%	$195.8753	$195.88	$195.90	$195.90
Purchase #6	$141.59	8.243%	$153.2613	$153.26	$153.25	$153.30
Purchase #7	$142.51	5.266%	$150.0146	$150.01	$150.00	$150.00
7 purchase totals =	$867.91		$924.7024	$924.70	$924.70	$924.70