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	$249.58	9.814%	$274.0738	$274.07	$274.05	$274.10
Purchase #2	$46.54	11.817%	$52.0396	$52.04	$52.05	$52.00
Purchase #3	$137.46	11.655%	$153.481	$153.48	$153.50	$153.50
Purchase #4	$76.47	6.681%	$81.579	$81.58	$81.60	$81.60
Purchase #5	$51.78	9.259%	$56.5743	$56.57	$56.55	$56.60
Purchase #6	$250.28	13.573%	$284.2505	$284.25	$284.25	$284.30
Purchase #7	$130.85	9.150%	$142.8228	$142.82	$142.80	$142.80
7 purchase totals =	$942.96		$1,044.8210	$1,044.81	$1,044.80	$1,044.90