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	$85.85	4.541%	$89.7484	$89.75	$89.75	$89.70
Purchase #2	$167.62	10.861%	$185.8252	$185.83	$185.85	$185.80
Purchase #3	$136.76	12.338%	$153.6334	$153.63	$153.65	$153.60
Purchase #4	$209.44	6.381%	$222.8044	$222.80	$222.80	$222.80
Purchase #5	$66.68	10.572%	$73.7294	$73.73	$73.75	$73.70
Purchase #6	$32.44	3.676%	$33.6325	$33.63	$33.65	$33.60
Purchase #7	$145.78	7.629%	$156.9016	$156.90	$156.90	$156.90
7 purchase totals =	$844.57		$916.2749	$916.27	$916.35	$916.10