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	$240.97	13.473%	$273.4359	$273.44	$273.45	$273.40
Purchase #2	$22.31	9.634%	$24.4593	$24.46	$24.45	$24.50
Purchase #3	$96.38	9.632%	$105.6633	$105.66	$105.65	$105.70
Purchase #4	$72.54	10.120%	$79.881	$79.88	$79.90	$79.90
Purchase #5	$103.52	5.277%	$108.9828	$108.98	$109.00	$109.00
Purchase #6	$165.79	12.746%	$186.9216	$186.92	$186.90	$186.90
Purchase #7	$106.49	3.206%	$109.9041	$109.90	$109.90	$109.90
7 purchase totals =	$808.00		$889.2480	$889.24	$889.25	$889.30