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	$127.89	10.143%	$140.8619	$140.86	$140.85	$140.90
Purchase #2	$221.28	11.663%	$247.0879	$247.09	$247.10	$247.10
Purchase #3	$7.56	4.444%	$7.896	$7.90	$7.90	$7.90
Purchase #4	$88.73	9.755%	$97.3856	$97.39	$97.40	$97.40
Purchase #5	$84.26	5.644%	$89.0156	$89.02	$89.00	$89.00
Purchase #6	$84.83	6.179%	$90.0716	$90.07	$90.05	$90.10
Purchase #7	$79.62	6.828%	$85.0565	$85.06	$85.05	$85.10
7 purchase totals =	$694.17		$757.3751	$757.39	$757.35	$757.50