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	$198.89	12.400%	$223.5524	$223.55	$223.55	$223.60
Purchase #2	$82.39	3.857%	$85.5678	$85.57	$85.55	$85.60
Purchase #3	$143.51	12.490%	$161.4344	$161.43	$161.45	$161.40
Purchase #4	$40.27	12.188%	$45.1781	$45.18	$45.20	$45.20
Purchase #5	$86.39	7.650%	$92.9988	$93.00	$93.00	$93.00
Purchase #6	$94.86	10.741%	$105.0489	$105.05	$105.05	$105.00
Purchase #7	$171.27	3.382%	$177.0624	$177.06	$177.05	$177.10
7 purchase totals =	$817.58		$890.8428	$890.84	$890.85	$890.90