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	$63.73	3.395%	$65.8936	$65.89	$65.90	$65.90
Purchase #2	$250.76	3.761%	$260.1911	$260.19	$260.20	$260.20
Purchase #3	$19.75	8.270%	$21.3833	$21.38	$21.40	$21.40
Purchase #4	$41.48	3.415%	$42.8965	$42.90	$42.90	$42.90
Purchase #5	$147.54	12.465%	$165.9309	$165.93	$165.95	$165.90
Purchase #6	$65.91	9.259%	$72.0126	$72.01	$72.00	$72.00
Purchase #7	$46.99	8.289%	$50.885	$50.89	$50.90	$50.90
7 purchase totals =	$636.16		$679.1930	$679.19	$679.25	$679.20