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	$134.43	7.770%	$144.8752	$144.88	$144.90	$144.90
Purchase #2	$52.57	12.632%	$59.2106	$59.21	$59.20	$59.20
Purchase #3	$40.91	11.336%	$45.5476	$45.55	$45.55	$45.50
Purchase #4	$182.63	8.738%	$198.5882	$198.59	$198.60	$198.60
Purchase #5	$232.82	13.412%	$264.0458	$264.05	$264.05	$264.00
Purchase #6	$186.29	7.494%	$200.2506	$200.25	$200.25	$200.30
Purchase #7	$19.41	6.196%	$20.6126	$20.61	$20.60	$20.60
7 purchase totals =	$849.06		$933.1306	$933.14	$933.15	$933.10