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	$127.44	9.340%	$139.3429	$139.34	$139.35	$139.30
Purchase #2	$137.42	12.364%	$154.4106	$154.41	$154.40	$154.40
Purchase #3	$37.54	13.289%	$42.5287	$42.53	$42.55	$42.50
Purchase #4	$78.83	9.515%	$86.3307	$86.33	$86.35	$86.30
Purchase #5	$160.56	11.646%	$179.2588	$179.26	$179.25	$179.30
Purchase #6	$241.61	10.542%	$267.0805	$267.08	$267.10	$267.10
Purchase #7	$12.95	11.813%	$14.4798	$14.48	$14.50	$14.50
7 purchase totals =	$796.35		$883.4320	$883.43	$883.50	$883.40