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	$32.41	7.742%	$34.9192	$34.92	$34.90	$34.90
Purchase #2	$202.40	6.350%	$215.2524	$215.25	$215.25	$215.30
Purchase #3	$172.42	5.815%	$182.4462	$182.45	$182.45	$182.40
Purchase #4	$168.40	8.821%	$183.2546	$183.25	$183.25	$183.30
Purchase #5	$222.80	9.298%	$243.5159	$243.52	$243.50	$243.50
Purchase #6	$50.99	11.256%	$56.7294	$56.73	$56.75	$56.70
Purchase #7	$92.84	10.317%	$102.4183	$102.42	$102.40	$102.40
7 purchase totals =	$942.26		$1,018.5360	$1,018.54	$1,018.50	$1,018.50