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	$24.51	9.573%	$26.8563	$26.86	$26.85	$26.90
Purchase #2	$160.46	3.659%	$166.3312	$166.33	$166.35	$166.30
Purchase #3	$185.67	6.678%	$198.069	$198.07	$198.05	$198.10
Purchase #4	$161.25	12.874%	$182.0093	$182.01	$182.00	$182.00
Purchase #5	$128.84	11.481%	$143.6321	$143.63	$143.65	$143.60
Purchase #6	$149.25	12.489%	$167.8898	$167.89	$167.90	$167.90
Purchase #7	$238.34	7.784%	$256.8924	$256.89	$256.90	$256.90
7 purchase totals =	$1,048.32		$1,141.6801	$1,141.68	$1,141.70	$1,141.70