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	$232.43	4.155%	$242.0875	$242.09	$242.10	$242.10
Purchase #2	$59.33	8.262%	$64.2318	$64.23	$64.25	$64.20
Purchase #3	$18.88	13.791%	$21.4837	$21.48	$21.50	$21.50
Purchase #4	$169.97	5.629%	$179.5376	$179.54	$179.55	$179.50
Purchase #5	$16.89	9.529%	$18.4994	$18.50	$18.50	$18.50
Purchase #6	$57.71	12.689%	$65.0328	$65.03	$65.05	$65.00
Purchase #7	$150.61	11.697%	$168.2269	$168.23	$168.25	$168.20
7 purchase totals =	$705.82		$759.0997	$759.10	$759.20	$759.00