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	$19.50	5.721%	$20.6156	$20.62	$20.60	$20.60
Purchase #2	$130.63	11.218%	$145.2841	$145.28	$145.30	$145.30
Purchase #3	$180.79	8.621%	$196.3759	$196.38	$196.40	$196.40
Purchase #4	$111.69	12.379%	$125.5161	$125.52	$125.50	$125.50
Purchase #5	$155.99	8.824%	$169.7546	$169.75	$169.75	$169.80
Purchase #6	$203.89	12.700%	$229.784	$229.78	$229.80	$229.80
Purchase #7	$49.97	10.827%	$55.3803	$55.38	$55.40	$55.40
7 purchase totals =	$852.46		$942.7106	$942.71	$942.75	$942.80