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	$112.84	6.714%	$120.4161	$120.42	$120.40	$120.40
Purchase #2	$174.33	10.678%	$192.945	$192.95	$192.95	$192.90
Purchase #3	$102.77	6.354%	$109.3	$109.30	$109.30	$109.30
Purchase #4	$121.28	12.259%	$136.1477	$136.15	$136.15	$136.10
Purchase #5	$114.89	3.790%	$119.2443	$119.24	$119.25	$119.20
Purchase #6	$45.25	9.587%	$49.5881	$49.59	$49.60	$49.60
Purchase #7	$182.36	7.516%	$196.0662	$196.07	$196.05	$196.10
7 purchase totals =	$853.72		$923.7074	$923.72	$923.70	$923.60