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	$155.98	12.287%	$175.1453	$175.15	$175.15	$175.10
Purchase #2	$250.55	9.566%	$274.5176	$274.52	$274.50	$274.50
Purchase #3	$189.63	10.604%	$209.7384	$209.74	$209.75	$209.70
Purchase #4	$97.27	7.650%	$104.7112	$104.71	$104.70	$104.70
Purchase #5	$43.64	9.738%	$47.8897	$47.89	$47.90	$47.90
Purchase #6	$172.46	3.375%	$178.2805	$178.28	$178.30	$178.30
Purchase #7	$13.74	11.225%	$15.2823	$15.28	$15.30	$15.30
7 purchase totals =	$923.27		$1,005.5650	$1,005.57	$1,005.60	$1,005.50