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	$35.29	6.367%	$37.5369	$37.54	$37.55	$37.50
Purchase #2	$124.72	4.575%	$130.4259	$130.43	$130.45	$130.40
Purchase #3	$52.44	10.519%	$57.9562	$57.96	$57.95	$58.00
Purchase #4	$213.32	10.384%	$235.4711	$235.47	$235.45	$235.50
Purchase #5	$217.98	7.119%	$233.498	$233.50	$233.50	$233.50
Purchase #6	$90.98	5.313%	$95.8138	$95.81	$95.80	$95.80
Purchase #7	$47.55	9.742%	$52.1823	$52.18	$52.20	$52.20
7 purchase totals =	$782.28		$842.8842	$842.89	$842.90	$842.90