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	$89.30	8.214%	$96.6351	$96.64	$96.65	$96.60
Purchase #2	$55.53	6.392%	$59.0795	$59.08	$59.10	$59.10
Purchase #3	$221.54	6.364%	$235.6388	$235.64	$235.65	$235.60
Purchase #4	$80.59	11.458%	$89.824	$89.82	$89.80	$89.80
Purchase #5	$156.62	8.195%	$169.455	$169.46	$169.45	$169.50
Purchase #6	$23.61	8.473%	$25.6105	$25.61	$25.60	$25.60
Purchase #7	$134.86	13.249%	$152.7276	$152.73	$152.75	$152.70
7 purchase totals =	$762.05		$828.9705	$828.98	$829.00	$828.90