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	$80.30	4.427%	$83.8549	$83.85	$83.85	$83.90
Purchase #2	$126.60	10.652%	$140.0854	$140.09	$140.10	$140.10
Purchase #3	$232.69	11.419%	$259.2609	$259.26	$259.25	$259.30
Purchase #4	$87.84	7.597%	$94.5132	$94.51	$94.50	$94.50
Purchase #5	$128.29	11.167%	$142.6161	$142.62	$142.60	$142.60
Purchase #6	$31.28	7.278%	$33.5566	$33.56	$33.55	$33.60
Purchase #7	$62.43	8.515%	$67.7459	$67.75	$67.75	$67.70
7 purchase totals =	$749.43		$821.6330	$821.64	$821.60	$821.70