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	$76.88	13.613%	$87.3457	$87.35	$87.35	$87.30
Purchase #2	$25.65	7.364%	$27.5389	$27.54	$27.55	$27.50
Purchase #3	$242.33	13.439%	$274.8967	$274.90	$274.90	$274.90
Purchase #4	$182.86	12.422%	$205.5749	$205.57	$205.55	$205.60
Purchase #5	$87.79	3.528%	$90.8872	$90.89	$90.90	$90.90
Purchase #6	$164.73	11.795%	$184.1599	$184.16	$184.15	$184.20
Purchase #7	$191.76	10.766%	$212.4049	$212.40	$212.40	$212.40
7 purchase totals =	$972.00		$1,082.8082	$1,082.81	$1,082.80	$1,082.80