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	$159.64	12.560%	$179.6908	$179.69	$179.70	$179.70
Purchase #2	$30.76	11.610%	$34.3312	$34.33	$34.35	$34.30
Purchase #3	$126.30	3.756%	$131.0438	$131.04	$131.05	$131.00
Purchase #4	$44.87	12.710%	$50.573	$50.57	$50.55	$50.60
Purchase #5	$126.93	8.666%	$137.9298	$137.93	$137.95	$137.90
Purchase #6	$174.72	3.299%	$180.484	$180.48	$180.50	$180.50
Purchase #7	$172.60	9.440%	$188.8934	$188.89	$188.90	$188.90
7 purchase totals =	$835.82		$902.9460	$902.93	$903.00	$902.90