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	$109.46	12.820%	$123.4928	$123.49	$123.50	$123.50
Purchase #2	$42.97	12.482%	$48.3335	$48.33	$48.35	$48.30
Purchase #3	$114.75	10.661%	$126.9835	$126.98	$127.00	$127.00
Purchase #4	$18.51	9.519%	$20.272	$20.27	$20.25	$20.30
Purchase #5	$161.86	8.762%	$176.0422	$176.04	$176.05	$176.00
Purchase #6	$199.65	8.293%	$216.207	$216.21	$216.20	$216.20
Purchase #7	$209.63	3.784%	$217.5624	$217.56	$217.55	$217.60
7 purchase totals =	$856.83		$928.8934	$928.88	$928.90	$928.90