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	$134.87	3.444%	$139.5149	$139.51	$139.50	$139.50
Purchase #2	$55.49	7.787%	$59.811	$59.81	$59.80	$59.80
Purchase #3	$34.81	6.628%	$37.1172	$37.12	$37.10	$37.10
Purchase #4	$98.38	9.284%	$107.5136	$107.51	$107.50	$107.50
Purchase #5	$50.38	10.446%	$55.6427	$55.64	$55.65	$55.60
Purchase #6	$205.76	12.807%	$232.1117	$232.11	$232.10	$232.10
Purchase #7	$181.77	3.617%	$188.3446	$188.34	$188.35	$188.30
7 purchase totals =	$761.46		$820.0557	$820.04	$820.00	$819.90