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	$70.77	11.124%	$78.6425	$78.64	$78.65	$78.60
Purchase #2	$45.47	3.661%	$47.1347	$47.13	$47.15	$47.10
Purchase #3	$184.82	8.434%	$200.4077	$200.41	$200.40	$200.40
Purchase #4	$88.36	11.656%	$98.6592	$98.66	$98.65	$98.70
Purchase #5	$122.50	7.656%	$131.8786	$131.88	$131.90	$131.90
Purchase #6	$86.52	10.734%	$95.8071	$95.81	$95.80	$95.80
Purchase #7	$117.88	12.222%	$132.2873	$132.29	$132.30	$132.30
7 purchase totals =	$716.32		$784.8171	$784.82	$784.85	$784.80