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	$42.43	3.190%	$43.7835	$43.78	$43.80	$43.80
Purchase #2	$24.56	9.689%	$26.9396	$26.94	$26.95	$26.90
Purchase #3	$25.82	9.560%	$28.2884	$28.29	$28.30	$28.30
Purchase #4	$136.72	8.222%	$147.9611	$147.96	$147.95	$148.00
Purchase #5	$38.97	8.443%	$42.2602	$42.26	$42.25	$42.30
Purchase #6	$101.89	9.564%	$111.6348	$111.63	$111.65	$111.60
Purchase #7	$191.57	12.568%	$215.6465	$215.65	$215.65	$215.60
7 purchase totals =	$561.96		$616.5141	$616.51	$616.55	$616.50