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	$11.56	6.123%	$12.2678	$12.27	$12.25	$12.30
Purchase #2	$236.37	11.107%	$262.6236	$262.62	$262.60	$262.60
Purchase #3	$103.96	7.314%	$111.5636	$111.56	$111.55	$111.60
Purchase #4	$188.74	7.483%	$202.8634	$202.86	$202.85	$202.90
Purchase #5	$34.96	3.466%	$36.1717	$36.17	$36.15	$36.20
Purchase #6	$209.36	6.750%	$223.4918	$223.49	$223.50	$223.50
Purchase #7	$74.31	11.749%	$83.0407	$83.04	$83.05	$83.00
7 purchase totals =	$859.26		$932.0226	$932.01	$931.95	$932.10