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	$129.48	7.392%	$139.0512	$139.05	$139.05	$139.10
Purchase #2	$237.45	7.850%	$256.0898	$256.09	$256.10	$256.10
Purchase #3	$88.82	11.829%	$99.3265	$99.33	$99.35	$99.30
Purchase #4	$36.37	8.589%	$39.4938	$39.49	$39.50	$39.50
Purchase #5	$222.97	11.150%	$247.8312	$247.83	$247.85	$247.80
Purchase #6	$170.79	3.148%	$176.1665	$176.17	$176.15	$176.20
Purchase #7	$155.26	9.446%	$169.9259	$169.93	$169.95	$169.90
7 purchase totals =	$1,041.14		$1,127.8849	$1,127.89	$1,127.95	$1,127.90