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	$35.95	11.756%	$40.1763	$40.18	$40.20	$40.20
Purchase #2	$81.40	4.786%	$85.2958	$85.30	$85.30	$85.30
Purchase #3	$221.74	9.332%	$242.4328	$242.43	$242.45	$242.40
Purchase #4	$139.46	11.691%	$155.7643	$155.76	$155.75	$155.80
Purchase #5	$105.68	4.164%	$110.0805	$110.08	$110.10	$110.10
Purchase #6	$97.83	11.736%	$109.3113	$109.31	$109.30	$109.30
Purchase #7	$235.59	3.328%	$243.4304	$243.43	$243.45	$243.40
7 purchase totals =	$917.65		$986.4914	$986.49	$986.55	$986.50