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	$174.58	5.591%	$184.3408	$184.34	$184.35	$184.30
Purchase #2	$117.84	11.711%	$131.6402	$131.64	$131.65	$131.60
Purchase #3	$166.93	12.622%	$187.9999	$188.00	$188.00	$188.00
Purchase #4	$20.40	11.568%	$22.7599	$22.76	$22.75	$22.80
Purchase #5	$89.37	12.573%	$100.6065	$100.61	$100.60	$100.60
Purchase #6	$40.70	5.161%	$42.8005	$42.80	$42.80	$42.80
Purchase #7	$39.98	13.596%	$45.4157	$45.42	$45.40	$45.40
7 purchase totals =	$649.80		$715.5635	$715.57	$715.55	$715.50