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	$37.93	12.435%	$42.6466	$42.65	$42.65	$42.60
Purchase #2	$50.63	8.799%	$55.0849	$55.08	$55.10	$55.10
Purchase #3	$246.60	3.612%	$255.5072	$255.51	$255.50	$255.50
Purchase #4	$67.94	12.709%	$76.5745	$76.57	$76.55	$76.60
Purchase #5	$213.96	6.471%	$227.8054	$227.81	$227.80	$227.80
Purchase #6	$5.62	11.767%	$6.2813	$6.28	$6.30	$6.30
Purchase #7	$247.65	12.670%	$279.0273	$279.03	$279.05	$279.00
7 purchase totals =	$870.33		$942.9272	$942.93	$942.95	$942.90