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	$125.92	11.448%	$140.3353	$140.34	$140.35	$140.30
Purchase #2	$247.51	9.347%	$270.6448	$270.64	$270.65	$270.60
Purchase #3	$49.52	8.812%	$53.8837	$53.88	$53.90	$53.90
Purchase #4	$243.45	12.658%	$274.2659	$274.27	$274.25	$274.30
Purchase #5	$144.81	10.806%	$160.4582	$160.46	$160.45	$160.50
Purchase #6	$72.75	7.300%	$78.0608	$78.06	$78.05	$78.10
Purchase #7	$82.50	8.530%	$89.5373	$89.54	$89.55	$89.50
7 purchase totals =	$966.46		$1,067.1860	$1,067.19	$1,067.20	$1,067.20