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	$171.40	9.578%	$187.8167	$187.82	$187.80	$187.80
Purchase #2	$123.60	4.282%	$128.8926	$128.89	$128.90	$128.90
Purchase #3	$84.54	9.181%	$92.3016	$92.30	$92.30	$92.30
Purchase #4	$152.75	10.407%	$168.6467	$168.65	$168.65	$168.60
Purchase #5	$180.48	8.620%	$196.0374	$196.04	$196.05	$196.00
Purchase #6	$53.60	3.832%	$55.654	$55.65	$55.65	$55.70
Purchase #7	$113.84	13.759%	$129.5032	$129.50	$129.50	$129.50
7 purchase totals =	$880.21		$958.8522	$958.85	$958.85	$958.80