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	$59.45	8.128%	$64.2821	$64.28	$64.30	$64.30
Purchase #2	$235.98	4.176%	$245.8345	$245.83	$245.85	$245.80
Purchase #3	$176.33	3.273%	$182.1013	$182.10	$182.10	$182.10
Purchase #4	$72.56	13.530%	$82.3774	$82.38	$82.40	$82.40
Purchase #5	$176.82	10.167%	$194.7973	$194.80	$194.80	$194.80
Purchase #6	$243.59	8.273%	$263.7422	$263.74	$263.75	$263.70
Purchase #7	$140.90	4.688%	$147.5054	$147.51	$147.50	$147.50
7 purchase totals =	$1,105.63		$1,180.6402	$1,180.64	$1,180.70	$1,180.60