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	$35.79	9.796%	$39.296	$39.30	$39.30	$39.30
Purchase #2	$35.66	6.452%	$37.9608	$37.96	$37.95	$38.00
Purchase #3	$163.74	3.692%	$169.7853	$169.79	$169.80	$169.80
Purchase #4	$139.29	8.455%	$151.067	$151.07	$151.05	$151.10
Purchase #5	$63.49	11.849%	$71.0129	$71.01	$71.00	$71.00
Purchase #6	$146.47	12.460%	$164.7202	$164.72	$164.70	$164.70
Purchase #7	$206.83	7.794%	$222.9503	$222.95	$222.95	$223.00
7 purchase totals =	$791.27		$856.7925	$856.80	$856.75	$856.90