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	$80.94	13.451%	$91.8272	$91.83	$91.85	$91.80
Purchase #2	$153.93	9.263%	$168.1885	$168.19	$168.20	$168.20
Purchase #3	$183.71	9.138%	$200.4974	$200.50	$200.50	$200.50
Purchase #4	$78.37	5.798%	$82.9139	$82.91	$82.90	$82.90
Purchase #5	$64.91	9.761%	$71.2459	$71.25	$71.25	$71.20
Purchase #6	$58.71	9.265%	$64.1495	$64.15	$64.15	$64.10
Purchase #7	$69.77	12.752%	$78.6671	$78.67	$78.65	$78.70
7 purchase totals =	$690.34		$757.4895	$757.50	$757.50	$757.40