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	$165.29	3.606%	$171.2504	$171.25	$171.25	$171.30
Purchase #2	$43.31	9.235%	$47.3097	$47.31	$47.30	$47.30
Purchase #3	$96.68	7.398%	$103.8324	$103.83	$103.85	$103.80
Purchase #4	$125.86	9.495%	$137.8104	$137.81	$137.80	$137.80
Purchase #5	$32.33	3.567%	$33.4832	$33.48	$33.50	$33.50
Purchase #6	$138.45	10.280%	$152.6827	$152.68	$152.70	$152.70
Purchase #7	$179.80	10.701%	$199.0404	$199.04	$199.05	$199.00
7 purchase totals =	$781.72		$845.4092	$845.40	$845.45	$845.40