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	$96.76	4.153%	$100.7784	$100.78	$100.80	$100.80
Purchase #2	$235.46	3.329%	$243.2985	$243.30	$243.30	$243.30
Purchase #3	$38.95	4.299%	$40.6245	$40.62	$40.60	$40.60
Purchase #4	$203.25	9.156%	$221.8596	$221.86	$221.85	$221.90
Purchase #5	$161.84	11.645%	$180.6863	$180.69	$180.70	$180.70
Purchase #6	$25.87	6.504%	$27.5526	$27.55	$27.55	$27.60
Purchase #7	$156.83	13.688%	$178.2969	$178.30	$178.30	$178.30
7 purchase totals =	$918.96		$993.0968	$993.10	$993.10	$993.20