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	$47.83	13.401%	$54.2397	$54.24	$54.25	$54.20
Purchase #2	$140.51	8.704%	$152.74	$152.74	$152.75	$152.70
Purchase #3	$152.74	12.557%	$171.9196	$171.92	$171.90	$171.90
Purchase #4	$78.39	7.126%	$83.9761	$83.98	$84.00	$84.00
Purchase #5	$102.99	6.757%	$109.949	$109.95	$109.95	$109.90
Purchase #6	$114.93	3.489%	$118.9399	$118.94	$118.95	$118.90
Purchase #7	$86.25	7.753%	$92.937	$92.94	$92.95	$92.90
7 purchase totals =	$723.64		$784.7013	$784.71	$784.75	$784.50