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	$128.74	3.156%	$132.803	$132.80	$132.80	$132.80
Purchase #2	$115.77	9.697%	$126.9962	$127.00	$127.00	$127.00
Purchase #3	$176.73	13.664%	$200.8784	$200.88	$200.90	$200.90
Purchase #4	$184.35	13.140%	$208.5736	$208.57	$208.55	$208.60
Purchase #5	$222.68	7.311%	$238.9601	$238.96	$238.95	$239.00
Purchase #6	$213.83	7.475%	$229.8138	$229.81	$229.80	$229.80
Purchase #7	$222.50	9.573%	$243.7999	$243.80	$243.80	$243.80
7 purchase totals =	$1,264.60		$1,381.8250	$1,381.82	$1,381.80	$1,381.90