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	$73.29	9.783%	$80.46	$80.46	$80.45	$80.50
Purchase #2	$142.50	5.385%	$150.1736	$150.17	$150.15	$150.20
Purchase #3	$15.88	13.700%	$18.0556	$18.06	$18.05	$18.10
Purchase #4	$147.84	8.337%	$160.1654	$160.17	$160.15	$160.20
Purchase #5	$144.82	11.112%	$160.9124	$160.91	$160.90	$160.90
Purchase #6	$150.76	13.754%	$171.4955	$171.50	$171.50	$171.50
Purchase #7	$205.28	9.460%	$224.6995	$224.70	$224.70	$224.70
7 purchase totals =	$880.37		$965.9620	$965.97	$965.90	$966.10