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	$110.92	6.186%	$117.7815	$117.78	$117.80	$117.80
Purchase #2	$38.81	6.779%	$41.4409	$41.44	$41.45	$41.40
Purchase #3	$84.74	3.367%	$87.5932	$87.59	$87.60	$87.60
Purchase #4	$127.46	11.340%	$141.914	$141.91	$141.90	$141.90
Purchase #5	$209.50	7.559%	$225.3361	$225.34	$225.35	$225.30
Purchase #6	$94.76	7.203%	$101.5856	$101.59	$101.60	$101.60
Purchase #7	$75.39	3.660%	$78.1493	$78.15	$78.15	$78.10
7 purchase totals =	$741.58		$793.8006	$793.80	$793.85	$793.70