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	$25.92	10.334%	$28.5986	$28.60	$28.60	$28.60
Purchase #2	$42.91	11.229%	$47.7284	$47.73	$47.75	$47.70
Purchase #3	$225.64	12.820%	$254.567	$254.57	$254.55	$254.60
Purchase #4	$197.31	12.732%	$222.4315	$222.43	$222.45	$222.40
Purchase #5	$126.94	7.577%	$136.5582	$136.56	$136.55	$136.60
Purchase #6	$245.53	10.659%	$271.701	$271.70	$271.70	$271.70
Purchase #7	$179.46	3.241%	$185.2763	$185.28	$185.30	$185.30
7 purchase totals =	$1,043.71		$1,146.8610	$1,146.87	$1,146.90	$1,146.90