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	$47.41	6.621%	$50.549	$50.55	$50.55	$50.50
Purchase #2	$134.32	11.709%	$150.0475	$150.05	$150.05	$150.00
Purchase #3	$203.26	9.616%	$222.8055	$222.81	$222.80	$222.80
Purchase #4	$141.29	13.119%	$159.8258	$159.83	$159.85	$159.80
Purchase #5	$210.93	8.699%	$229.2788	$229.28	$229.30	$229.30
Purchase #6	$125.54	13.366%	$142.3197	$142.32	$142.30	$142.30
Purchase #7	$21.30	9.523%	$23.3284	$23.33	$23.35	$23.30
7 purchase totals =	$884.05		$978.1547	$978.17	$978.20	$978.00