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	$45.74	3.469%	$47.3267	$47.33	$47.35	$47.30
Purchase #2	$184.92	8.386%	$200.4274	$200.43	$200.45	$200.40
Purchase #3	$202.30	7.159%	$216.7827	$216.78	$216.80	$216.80
Purchase #4	$154.59	7.747%	$166.5661	$166.57	$166.55	$166.60
Purchase #5	$139.82	12.171%	$156.8375	$156.84	$156.85	$156.80
Purchase #6	$66.50	9.664%	$72.9266	$72.93	$72.95	$72.90
Purchase #7	$202.78	6.448%	$215.8553	$215.86	$215.85	$215.90
7 purchase totals =	$996.65		$1,076.7223	$1,076.74	$1,076.80	$1,076.70