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	$5.83	12.250%	$6.5442	$6.54	$6.55	$6.50
Purchase #2	$189.29	5.289%	$199.3015	$199.30	$199.30	$199.30
Purchase #3	$70.56	10.480%	$77.9547	$77.95	$77.95	$78.00
Purchase #4	$34.48	7.390%	$37.0281	$37.03	$37.05	$37.00
Purchase #5	$38.55	12.203%	$43.2543	$43.25	$43.25	$43.30
Purchase #6	$28.52	11.355%	$31.7584	$31.76	$31.75	$31.80
Purchase #7	$137.63	9.448%	$150.6333	$150.63	$150.65	$150.60
7 purchase totals =	$504.86		$546.4745	$546.46	$546.50	$546.50