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	$121.59	8.187%	$131.5446	$131.54	$131.55	$131.50
Purchase #2	$171.90	4.446%	$179.5427	$179.54	$179.55	$179.50
Purchase #3	$214.81	12.529%	$241.7235	$241.72	$241.70	$241.70
Purchase #4	$123.33	6.806%	$131.7238	$131.72	$131.70	$131.70
Purchase #5	$183.81	8.659%	$199.7261	$199.73	$199.75	$199.70
Purchase #6	$93.39	6.407%	$99.3735	$99.37	$99.35	$99.40
Purchase #7	$19.90	4.183%	$20.7324	$20.73	$20.75	$20.70
7 purchase totals =	$928.73		$1,004.3666	$1,004.35	$1,004.35	$1,004.20