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	$97.91	11.642%	$109.3087	$109.31	$109.30	$109.30
Purchase #2	$208.75	4.375%	$217.8828	$217.88	$217.90	$217.90
Purchase #3	$128.63	4.595%	$134.5405	$134.54	$134.55	$134.50
Purchase #4	$165.84	12.257%	$186.167	$186.17	$186.15	$186.20
Purchase #5	$187.37	10.260%	$206.5942	$206.59	$206.60	$206.60
Purchase #6	$84.40	6.145%	$89.5864	$89.59	$89.60	$89.60
Purchase #7	$250.93	10.296%	$276.7658	$276.77	$276.75	$276.80
7 purchase totals =	$1,123.83		$1,220.8454	$1,220.85	$1,220.85	$1,220.90