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	$62.83	6.769%	$67.083	$67.08	$67.10	$67.10
Purchase #2	$85.56	3.769%	$88.7848	$88.78	$88.80	$88.80
Purchase #3	$47.64	13.694%	$54.1638	$54.16	$54.15	$54.20
Purchase #4	$113.84	10.854%	$126.1962	$126.20	$126.20	$126.20
Purchase #5	$157.50	12.256%	$176.8032	$176.80	$176.80	$176.80
Purchase #6	$8.26	7.686%	$8.8949	$8.89	$8.90	$8.90
Purchase #7	$85.79	4.809%	$89.9156	$89.92	$89.90	$89.90
7 purchase totals =	$561.42		$611.8415	$611.83	$611.85	$611.90