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	$188.34	9.123%	$205.5223	$205.52	$205.50	$205.50
Purchase #2	$244.25	8.702%	$265.5046	$265.50	$265.50	$265.50
Purchase #3	$82.72	12.288%	$92.8846	$92.88	$92.90	$92.90
Purchase #4	$26.67	5.455%	$28.1248	$28.12	$28.10	$28.10
Purchase #5	$203.74	11.367%	$226.8991	$226.90	$226.90	$226.90
Purchase #6	$80.37	3.140%	$82.8936	$82.89	$82.90	$82.90
Purchase #7	$65.33	11.441%	$72.8044	$72.80	$72.80	$72.80
7 purchase totals =	$891.42		$974.6334	$974.61	$974.60	$974.60