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	$245.64	5.802%	$259.892	$259.89	$259.90	$259.90
Purchase #2	$244.84	6.799%	$261.4867	$261.49	$261.50	$261.50
Purchase #3	$105.52	11.504%	$117.659	$117.66	$117.65	$117.70
Purchase #4	$188.53	10.402%	$208.1409	$208.14	$208.15	$208.10
Purchase #5	$93.34	7.401%	$100.2481	$100.25	$100.25	$100.20
Purchase #6	$226.55	9.388%	$247.8185	$247.82	$247.80	$247.80
Purchase #7	$38.43	13.569%	$43.6446	$43.64	$43.65	$43.60
7 purchase totals =	$1,142.85		$1,238.8898	$1,238.89	$1,238.90	$1,238.80