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	$146.53	13.601%	$166.4595	$166.46	$166.45	$166.50
Purchase #2	$247.81	8.782%	$269.5727	$269.57	$269.55	$269.60
Purchase #3	$119.54	9.817%	$131.2752	$131.28	$131.30	$131.30
Purchase #4	$227.35	5.133%	$239.0199	$239.02	$239.00	$239.00
Purchase #5	$104.30	6.693%	$111.2808	$111.28	$111.30	$111.30
Purchase #6	$219.85	10.518%	$242.9738	$242.97	$242.95	$243.00
Purchase #7	$95.79	3.307%	$98.9578	$98.96	$98.95	$99.00
7 purchase totals =	$1,161.17		$1,259.5397	$1,259.54	$1,259.50	$1,259.70