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	$77.74	6.120%	$82.4977	$82.50	$82.50	$82.50
Purchase #2	$89.67	10.561%	$99.14	$99.14	$99.15	$99.10
Purchase #3	$113.90	4.376%	$118.8843	$118.88	$118.90	$118.90
Purchase #4	$227.67	4.562%	$238.0563	$238.06	$238.05	$238.10
Purchase #5	$246.80	7.680%	$265.7542	$265.75	$265.75	$265.80
Purchase #6	$224.68	9.199%	$245.3483	$245.35	$245.35	$245.30
Purchase #7	$205.42	11.342%	$228.7187	$228.72	$228.70	$228.70
7 purchase totals =	$1,185.88		$1,278.3995	$1,278.40	$1,278.40	$1,278.40