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	$13.95	11.131%	$15.5028	$15.50	$15.50	$15.50
Purchase #2	$131.73	11.815%	$147.2939	$147.29	$147.30	$147.30
Purchase #3	$130.70	8.763%	$142.1532	$142.15	$142.15	$142.20
Purchase #4	$137.34	12.458%	$154.4498	$154.45	$154.45	$154.40
Purchase #5	$73.66	11.867%	$82.4012	$82.40	$82.40	$82.40
Purchase #6	$201.93	10.504%	$223.1407	$223.14	$223.15	$223.10
Purchase #7	$178.64	11.119%	$198.503	$198.50	$198.50	$198.50
7 purchase totals =	$867.95		$963.4446	$963.43	$963.45	$963.40