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	$117.89	11.551%	$131.5075	$131.51	$131.50	$131.50
Purchase #2	$27.61	13.842%	$31.4318	$31.43	$31.45	$31.40
Purchase #3	$186.66	9.834%	$205.0161	$205.02	$205.00	$205.00
Purchase #4	$82.40	11.404%	$91.7969	$91.80	$91.80	$91.80
Purchase #5	$89.75	12.497%	$100.9661	$100.97	$100.95	$101.00
Purchase #6	$142.29	13.102%	$160.9328	$160.93	$160.95	$160.90
Purchase #7	$93.51	10.682%	$103.4987	$103.50	$103.50	$103.50
7 purchase totals =	$740.11		$825.1499	$825.16	$825.15	$825.10