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	$57.47	6.514%	$61.2136	$61.21	$61.20	$61.20
Purchase #2	$169.72	9.159%	$185.2647	$185.26	$185.25	$185.30
Purchase #3	$136.84	10.597%	$151.3409	$151.34	$151.35	$151.30
Purchase #4	$139.53	11.705%	$155.862	$155.86	$155.85	$155.90
Purchase #5	$45.91	9.712%	$50.3688	$50.37	$50.35	$50.40
Purchase #6	$162.51	3.652%	$168.4449	$168.44	$168.45	$168.40
Purchase #7	$149.66	11.178%	$166.389	$166.39	$166.40	$166.40
7 purchase totals =	$861.64		$938.8839	$938.87	$938.85	$938.90