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	$120.77	12.434%	$135.7865	$135.79	$135.80	$135.80
Purchase #2	$48.46	4.111%	$50.4522	$50.45	$50.45	$50.50
Purchase #3	$137.96	9.287%	$150.7723	$150.77	$150.75	$150.80
Purchase #4	$131.97	3.559%	$136.6668	$136.67	$136.65	$136.70
Purchase #5	$72.28	12.820%	$81.5463	$81.55	$81.55	$81.50
Purchase #6	$189.40	3.622%	$196.2601	$196.26	$196.25	$196.30
Purchase #7	$166.33	13.530%	$188.8344	$188.83	$188.85	$188.80
7 purchase totals =	$867.17		$940.3186	$940.32	$940.30	$940.40