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	$114.89	11.320%	$127.8955	$127.90	$127.90	$127.90
Purchase #2	$185.76	8.125%	$200.853	$200.85	$200.85	$200.90
Purchase #3	$111.37	10.676%	$123.2599	$123.26	$123.25	$123.30
Purchase #4	$68.42	9.682%	$75.0444	$75.04	$75.05	$75.00
Purchase #5	$221.30	8.666%	$240.4779	$240.48	$240.50	$240.50
Purchase #6	$232.26	11.818%	$259.7085	$259.71	$259.70	$259.70
Purchase #7	$124.31	13.793%	$141.4561	$141.46	$141.45	$141.50
7 purchase totals =	$1,058.31		$1,168.6953	$1,168.70	$1,168.70	$1,168.80