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	$82.74	9.172%	$90.3289	$90.33	$90.35	$90.30
Purchase #2	$35.40	12.157%	$39.7036	$39.70	$39.70	$39.70
Purchase #3	$91.75	3.109%	$94.6025	$94.60	$94.60	$94.60
Purchase #4	$136.76	10.287%	$150.8285	$150.83	$150.85	$150.80
Purchase #5	$136.60	5.334%	$143.8862	$143.89	$143.90	$143.90
Purchase #6	$128.35	6.755%	$137.02	$137.02	$137.00	$137.00
Purchase #7	$174.25	12.837%	$196.6185	$196.62	$196.60	$196.60
7 purchase totals =	$785.85		$852.9882	$852.99	$853.00	$852.90