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	$18.32	3.643%	$18.9874	$18.99	$19.00	$19.00
Purchase #2	$238.78	12.425%	$268.4484	$268.45	$268.45	$268.40
Purchase #3	$113.49	10.579%	$125.4961	$125.50	$125.50	$125.50
Purchase #4	$241.90	3.395%	$250.1125	$250.11	$250.10	$250.10
Purchase #5	$80.38	3.166%	$82.9248	$82.92	$82.90	$82.90
Purchase #6	$185.73	9.602%	$203.5638	$203.56	$203.55	$203.60
Purchase #7	$193.88	3.414%	$200.4991	$200.50	$200.50	$200.50
7 purchase totals =	$1,072.48		$1,150.0321	$1,150.03	$1,150.00	$1,150.00