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	$109.84	8.549%	$119.2302	$119.23	$119.25	$119.20
Purchase #2	$209.85	10.425%	$231.7269	$231.73	$231.75	$231.70
Purchase #3	$125.86	8.714%	$136.8274	$136.83	$136.85	$136.80
Purchase #4	$78.57	13.684%	$89.3215	$89.32	$89.30	$89.30
Purchase #5	$123.47	12.641%	$139.0778	$139.08	$139.10	$139.10
Purchase #6	$147.71	10.226%	$162.8148	$162.81	$162.80	$162.80
Purchase #7	$26.94	7.310%	$28.9093	$28.91	$28.90	$28.90
7 purchase totals =	$822.24		$907.9079	$907.91	$907.95	$907.80