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	$177.67	4.627%	$185.8908	$185.89	$185.90	$185.90
Purchase #2	$122.71	11.763%	$137.1444	$137.14	$137.15	$137.10
Purchase #3	$204.50	13.228%	$231.5513	$231.55	$231.55	$231.60
Purchase #4	$127.81	9.172%	$139.5327	$139.53	$139.55	$139.50
Purchase #5	$69.65	10.476%	$76.9465	$76.95	$76.95	$76.90
Purchase #6	$93.69	13.814%	$106.6323	$106.63	$106.65	$106.60
Purchase #7	$85.98	9.689%	$94.3106	$94.31	$94.30	$94.30
7 purchase totals =	$882.01		$972.0086	$972.00	$972.05	$971.90