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	$127.56	12.567%	$143.5905	$143.59	$143.60	$143.60
Purchase #2	$243.80	9.312%	$266.5027	$266.50	$266.50	$266.50
Purchase #3	$209.92	11.447%	$233.9495	$233.95	$233.95	$233.90
Purchase #4	$88.79	13.544%	$100.8157	$100.82	$100.80	$100.80
Purchase #5	$67.69	3.129%	$69.808	$69.81	$69.80	$69.80
Purchase #6	$36.62	7.758%	$39.461	$39.46	$39.45	$39.50
Purchase #7	$92.59	3.117%	$95.476	$95.48	$95.50	$95.50
7 purchase totals =	$866.97		$949.6034	$949.61	$949.60	$949.60