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	$136.34	11.135%	$151.5215	$151.52	$151.50	$151.50
Purchase #2	$54.45	10.752%	$60.3045	$60.30	$60.30	$60.30
Purchase #3	$134.79	10.311%	$148.6882	$148.69	$148.70	$148.70
Purchase #4	$224.90	9.282%	$245.7752	$245.78	$245.80	$245.80
Purchase #5	$140.28	10.765%	$155.3811	$155.38	$155.40	$155.40
Purchase #6	$91.88	11.376%	$102.3323	$102.33	$102.35	$102.30
Purchase #7	$134.51	3.559%	$139.2972	$139.30	$139.30	$139.30
7 purchase totals =	$917.15		$1,003.3000	$1,003.30	$1,003.35	$1,003.30