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	$76.73	7.524%	$82.5032	$82.50	$82.50	$82.50
Purchase #2	$224.38	11.337%	$249.818	$249.82	$249.80	$249.80
Purchase #3	$81.83	4.220%	$85.2832	$85.28	$85.30	$85.30
Purchase #4	$140.27	9.827%	$154.0543	$154.05	$154.05	$154.10
Purchase #5	$78.30	9.271%	$85.5592	$85.56	$85.55	$85.60
Purchase #6	$64.79	10.636%	$71.6811	$71.68	$71.70	$71.70
Purchase #7	$246.73	4.251%	$257.2185	$257.22	$257.20	$257.20
7 purchase totals =	$913.03		$986.1175	$986.11	$986.10	$986.20