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	$233.69	7.148%	$250.3942	$250.39	$250.40	$250.40
Purchase #2	$225.63	10.186%	$248.6127	$248.61	$248.60	$248.60
Purchase #3	$148.64	4.571%	$155.4343	$155.43	$155.45	$155.40
Purchase #4	$102.43	9.485%	$112.1455	$112.15	$112.15	$112.10
Purchase #5	$41.49	10.314%	$45.7693	$45.77	$45.75	$45.80
Purchase #6	$245.55	11.647%	$274.1492	$274.15	$274.15	$274.10
Purchase #7	$125.90	5.129%	$132.3574	$132.36	$132.35	$132.40
7 purchase totals =	$1,123.33		$1,218.8626	$1,218.86	$1,218.85	$1,218.80