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	$191.67	9.373%	$209.6352	$209.64	$209.65	$209.60
Purchase #2	$214.35	5.829%	$226.8445	$226.84	$226.85	$226.80
Purchase #3	$129.74	13.445%	$147.1835	$147.18	$147.20	$147.20
Purchase #4	$106.69	12.353%	$119.8694	$119.87	$119.85	$119.90
Purchase #5	$82.77	9.312%	$90.4775	$90.48	$90.50	$90.50
Purchase #6	$123.82	10.528%	$136.8558	$136.86	$136.85	$136.90
Purchase #7	$200.48	4.700%	$209.9026	$209.90	$209.90	$209.90
7 purchase totals =	$1,049.52		$1,140.7685	$1,140.77	$1,140.80	$1,140.80