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	$123.57	11.115%	$137.3048	$137.30	$137.30	$137.30
Purchase #2	$52.83	5.334%	$55.648	$55.65	$55.65	$55.60
Purchase #3	$33.34	13.180%	$37.7342	$37.73	$37.75	$37.70
Purchase #4	$107.92	6.498%	$114.9326	$114.93	$114.95	$114.90
Purchase #5	$114.27	9.696%	$125.3496	$125.35	$125.35	$125.30
Purchase #6	$175.72	13.179%	$198.8781	$198.88	$198.90	$198.90
Purchase #7	$139.42	9.544%	$152.7262	$152.73	$152.75	$152.70
7 purchase totals =	$747.07		$822.5735	$822.57	$822.65	$822.40